is assignment of variables

1.4 — Variable assignment and initialization

In the previous lesson ( 1.3 -- Introduction to objects and variables ), we covered how to define a variable that we can use to store values. In this lesson, we’ll explore how to actually put values into variables and use those values.

As a reminder, here’s a short snippet that first allocates a single integer variable named x , then allocates two more integer variables named y and z :

Variable assignment

After a variable has been defined, you can give it a value (in a separate statement) using the = operator . This process is called assignment , and the = operator is called the assignment operator .

By default, assignment copies the value on the right-hand side of the = operator to the variable on the left-hand side of the operator. This is called copy assignment .

Here’s an example where we use assignment twice:

This prints:

When we assign value 7 to variable width , the value 5 that was there previously is overwritten. Normal variables can only hold one value at a time.

One of the most common mistakes that new programmers make is to confuse the assignment operator ( = ) with the equality operator ( == ). Assignment ( = ) is used to assign a value to a variable. Equality ( == ) is used to test whether two operands are equal in value.

Initialization

One downside of assignment is that it requires at least two statements: one to define the variable, and another to assign the value.

These two steps can be combined. When an object is defined, you can optionally give it an initial value. The process of specifying an initial value for an object is called initialization , and the syntax used to initialize an object is called an initializer .

In the above initialization of variable width , { 5 } is the initializer, and 5 is the initial value.

Different forms of initialization

Initialization in C++ is surprisingly complex, so we’ll present a simplified view here.

There are 6 basic ways to initialize variables in C++:

You may see the above forms written with different spacing (e.g. int d{7}; ). Whether you use extra spaces for readability or not is a matter of personal preference.

Default initialization

When no initializer is provided (such as for variable a above), this is called default initialization . In most cases, default initialization performs no initialization, and leaves a variable with an indeterminate value.

We’ll discuss this case further in lesson ( 1.6 -- Uninitialized variables and undefined behavior ).

Copy initialization

When an initial value is provided after an equals sign, this is called copy initialization . This form of initialization was inherited from C.

Much like copy assignment, this copies the value on the right-hand side of the equals into the variable being created on the left-hand side. In the above snippet, variable width will be initialized with value 5 .

Copy initialization had fallen out of favor in modern C++ due to being less efficient than other forms of initialization for some complex types. However, C++17 remedied the bulk of these issues, and copy initialization is now finding new advocates. You will also find it used in older code (especially code ported from C), or by developers who simply think it looks more natural and is easier to read.

For advanced readers

Copy initialization is also used whenever values are implicitly copied or converted, such as when passing arguments to a function by value, returning from a function by value, or catching exceptions by value.

Direct initialization

When an initial value is provided inside parenthesis, this is called direct initialization .

Direct initialization was initially introduced to allow for more efficient initialization of complex objects (those with class types, which we’ll cover in a future chapter). Just like copy initialization, direct initialization had fallen out of favor in modern C++, largely due to being superseded by list initialization. However, we now know that list initialization has a few quirks of its own, and so direct initialization is once again finding use in certain cases.

Direct initialization is also used when values are explicitly cast to another type.

One of the reasons direct initialization had fallen out of favor is because it makes it hard to differentiate variables from functions. For example:

List initialization

The modern way to initialize objects in C++ is to use a form of initialization that makes use of curly braces. This is called list initialization (or uniform initialization or brace initialization ).

List initialization comes in three forms:

As an aside…

Prior to the introduction of list initialization, some types of initialization required using copy initialization, and other types of initialization required using direct initialization. List initialization was introduced to provide a more consistent initialization syntax (which is why it is sometimes called “uniform initialization”) that works in most cases.

Additionally, list initialization provides a way to initialize objects with a list of values (which is why it is called “list initialization”). We show an example of this in lesson 16.2 -- Introduction to std::vector and list constructors .

List initialization has an added benefit: “narrowing conversions” in list initialization are ill-formed. This means that if you try to brace initialize a variable using a value that the variable can not safely hold, the compiler is required to produce a diagnostic (usually an error). For example:

In the above snippet, we’re trying to assign a number (4.5) that has a fractional part (the .5 part) to an integer variable (which can only hold numbers without fractional parts).

Copy and direct initialization would simply drop the fractional part, resulting in the initialization of value 4 into variable width . Your compiler may optionally warn you about this, since losing data is rarely desired. However, with list initialization, your compiler is required to generate a diagnostic in such cases.

Conversions that can be done without potential data loss are allowed.

To summarize, list initialization is generally preferred over the other initialization forms because it works in most cases (and is therefore most consistent), it disallows narrowing conversions, and it supports initialization with lists of values (something we’ll cover in a future lesson). While you are learning, we recommend sticking with list initialization (or value initialization).

Best practice

Prefer direct list initialization (or value initialization) for initializing your variables.

Author’s note

Bjarne Stroustrup (creator of C++) and Herb Sutter (C++ expert) also recommend using list initialization to initialize your variables.

In modern C++, there are some cases where list initialization does not work as expected. We cover one such case in lesson 16.2 -- Introduction to std::vector and list constructors .

Because of such quirks, some experienced developers now advocate for using a mix of copy, direct, and list initialization, depending on the circumstance. Once you are familiar enough with the language to understand the nuances of each initialization type and the reasoning behind such recommendations, you can evaluate on your own whether you find these arguments persuasive.

Value initialization and zero initialization

When a variable is initialized using empty braces, value initialization takes place. In most cases, value initialization will initialize the variable to zero (or empty, if that’s more appropriate for a given type). In such cases where zeroing occurs, this is called zero initialization .

Q: When should I initialize with { 0 } vs {}?

Use an explicit initialization value if you’re actually using that value.

Use value initialization if the value is temporary and will be replaced.

Initialize your variables

Initialize your variables upon creation. You may eventually find cases where you want to ignore this advice for a specific reason (e.g. a performance critical section of code that uses a lot of variables), and that’s okay, as long as the choice is made deliberately.

Related content

For more discussion on this topic, Bjarne Stroustrup (creator of C++) and Herb Sutter (C++ expert) make this recommendation themselves here .

We explore what happens if you try to use a variable that doesn’t have a well-defined value in lesson 1.6 -- Uninitialized variables and undefined behavior .

Initialize your variables upon creation.

Initializing multiple variables

In the last section, we noted that it is possible to define multiple variables of the same type in a single statement by separating the names with a comma:

We also noted that best practice is to avoid this syntax altogether. However, since you may encounter other code that uses this style, it’s still useful to talk a little bit more about it, if for no other reason than to reinforce some of the reasons you should be avoiding it.

You can initialize multiple variables defined on the same line:

Unfortunately, there’s a common pitfall here that can occur when the programmer mistakenly tries to initialize both variables by using one initialization statement:

In the top statement, variable “a” will be left uninitialized, and the compiler may or may not complain. If it doesn’t, this is a great way to have your program intermittently crash or produce sporadic results. We’ll talk more about what happens if you use uninitialized variables shortly.

The best way to remember that this is wrong is to consider the case of direct initialization or brace initialization:

Because the parenthesis or braces are typically placed right next to the variable name, this makes it seem a little more clear that the value 5 is only being used to initialize variable b and d , not a or c .

Unused initialized variables warnings

Modern compilers will typically generate warnings if a variable is initialized but not used (since this is rarely desirable). And if “treat warnings as errors” is enabled, these warnings will be promoted to errors and cause the compilation to fail.

Consider the following innocent looking program:

When compiling this with the g++ compiler, the following error is generated:

and the program fails to compile.

There are a few easy ways to fix this.

• If the variable really is unused, then the easiest option is to remove the defintion of x (or comment it out). After all, if it’s not used, then removing it won’t affect anything.
• Another option is to simply use the variable somewhere:

But this requires some effort to write code that uses it, and has the downside of potentially changing your program’s behavior.

The [[maybe_unused]] attribute C++17

In some cases, neither of the above options are desirable. Consider the case where we have a bunch of math/physics values that we use in many different programs:

If we use these a lot, we probably have these saved somewhere and copy/paste/import them all together.

However, in any program where we don’t use all of these values, the compiler will complain about each variable that isn’t actually used. While we could go through and remove/comment out the unused ones for each program, this takes time and energy. And later if we need one that we’ve previously removed, we’ll have to go back and re-add it.

To address such cases, C++17 introduced the [[maybe_unused]] attribute, which allows us to tell the compiler that we’re okay with a variable being unused. The compiler will not generate unused variable warnings for such variables.

The following program should generate no warnings/errors:

Additionally, the compiler will likely optimize these variables out of the program, so they have no performance impact.

In future lessons, we’ll often define variables we don’t use again, in order to demonstrate certain concepts. Making use of [[maybe_unused]] allows us to do so without compilation warnings/errors.

Question #1

What is the difference between initialization and assignment?

Show Solution

Initialization gives a variable an initial value at the point when it is created. Assignment gives a variable a value at some point after the variable is created.

Question #2

What form of initialization should you prefer when you want to initialize a variable with a specific value?

Direct list initialization (aka. direct brace initialization).

Question #3

What are default initialization and value initialization? What is the behavior of each? Which should you prefer?

Default initialization is when a variable initialization has no initializer (e.g. int x; ). In most cases, the variable is left with an indeterminate value.

Value initialization is when a variable initialization has an empty brace (e.g. int x{}; ). In most cases this will perform zero-initialization.

You should prefer value initialization to default initialization.

Python Numerical Methods

This notebook contains an excerpt from the Python Programming and Numerical Methods - A Guide for Engineers and Scientists , the content is also available at Berkeley Python Numerical Methods .

The copyright of the book belongs to Elsevier. We also have this interactive book online for a better learning experience. The code is released under the MIT license . If you find this content useful, please consider supporting the work on Elsevier or Amazon !

< 2.0 Variables and Basic Data Structures | Contents | 2.2 Data Structure - Strings >

Variables and Assignment ¶

When programming, it is useful to be able to store information in variables. A variable is a string of characters and numbers associated with a piece of information. The assignment operator , denoted by the “=” symbol, is the operator that is used to assign values to variables in Python. The line x=1 takes the known value, 1, and assigns that value to the variable with name “x”. After executing this line, this number will be stored into this variable. Until the value is changed or the variable deleted, the character x behaves like the value 1.

TRY IT! Assign the value 2 to the variable y. Multiply y by 3 to show that it behaves like the value 2.

A variable is more like a container to store the data in the computer’s memory, the name of the variable tells the computer where to find this value in the memory. For now, it is sufficient to know that the notebook has its own memory space to store all the variables in the notebook. As a result of the previous example, you will see the variable “x” and “y” in the memory. You can view a list of all the variables in the notebook using the magic command %whos .

TRY IT! List all the variables in this notebook

Note that the equal sign in programming is not the same as a truth statement in mathematics. In math, the statement x = 2 declares the universal truth within the given framework, x is 2 . In programming, the statement x=2 means a known value is being associated with a variable name, store 2 in x. Although it is perfectly valid to say 1 = x in mathematics, assignments in Python always go left : meaning the value to the right of the equal sign is assigned to the variable on the left of the equal sign. Therefore, 1=x will generate an error in Python. The assignment operator is always last in the order of operations relative to mathematical, logical, and comparison operators.

TRY IT! The mathematical statement x=x+1 has no solution for any value of x . In programming, if we initialize the value of x to be 1, then the statement makes perfect sense. It means, “Add x and 1, which is 2, then assign that value to the variable x”. Note that this operation overwrites the previous value stored in x .

There are some restrictions on the names variables can take. Variables can only contain alphanumeric characters (letters and numbers) as well as underscores. However, the first character of a variable name must be a letter or underscores. Spaces within a variable name are not permitted, and the variable names are case-sensitive (e.g., x and X will be considered different variables).

TIP! Unlike in pure mathematics, variables in programming almost always represent something tangible. It may be the distance between two points in space or the number of rabbits in a population. Therefore, as your code becomes increasingly complicated, it is very important that your variables carry a name that can easily be associated with what they represent. For example, the distance between two points in space is better represented by the variable dist than x , and the number of rabbits in a population is better represented by nRabbits than y .

Note that when a variable is assigned, it has no memory of how it was assigned. That is, if the value of a variable, y , is constructed from other variables, like x , reassigning the value of x will not change the value of y .

EXAMPLE: What value will y have after the following lines of code are executed?

WARNING! You can overwrite variables or functions that have been stored in Python. For example, the command help = 2 will store the value 2 in the variable with name help . After this assignment help will behave like the value 2 instead of the function help . Therefore, you should always be careful not to give your variables the same name as built-in functions or values.

TIP! Now that you know how to assign variables, it is important that you learn to never leave unassigned commands. An unassigned command is an operation that has a result, but that result is not assigned to a variable. For example, you should never use 2+2 . You should instead assign it to some variable x=2+2 . This allows you to “hold on” to the results of previous commands and will make your interaction with Python must less confusing.

You can clear a variable from the notebook using the del function. Typing del x will clear the variable x from the workspace. If you want to remove all the variables in the notebook, you can use the magic command %reset .

In mathematics, variables are usually associated with unknown numbers; in programming, variables are associated with a value of a certain type. There are many data types that can be assigned to variables. A data type is a classification of the type of information that is being stored in a variable. The basic data types that you will utilize throughout this book are boolean, int, float, string, list, tuple, dictionary, set. A formal description of these data types is given in the following sections.

Python Variables and Assignment

Python variables, variable assignment rules, every value has a type, memory and the garbage collector, variable swap, variable names are superficial labels, assignment = is shallow, decomp by var.

• Hands-on Python Tutorial »
• 1. Beginning With Python »

1.6. Variables and Assignment ¶

Each set-off line in this section should be tried in the Shell.

Nothing is displayed by the interpreter after this entry, so it is not clear anything happened. Something has happened. This is an assignment statement , with a variable , width , on the left. A variable is a name for a value. An assignment statement associates a variable name on the left of the equal sign with the value of an expression calculated from the right of the equal sign. Enter

Once a variable is assigned a value, the variable can be used in place of that value. The response to the expression width is the same as if its value had been entered.

The interpreter does not print a value after an assignment statement because the value of the expression on the right is not lost. It can be recovered if you like, by entering the variable name and we did above.

Try each of the following lines:

The equal sign is an unfortunate choice of symbol for assignment, since Python’s usage is not the mathematical usage of the equal sign. If the symbol ↤ had appeared on keyboards in the early 1990’s, it would probably have been used for assignment instead of =, emphasizing the asymmetry of assignment. In mathematics an equation is an assertion that both sides of the equal sign are already, in fact, equal . A Python assignment statement forces the variable on the left hand side to become associated with the value of the expression on the right side. The difference from the mathematical usage can be illustrated. Try:

so this is not equivalent in Python to width = 10 . The left hand side must be a variable, to which the assignment is made. Reversed, we get a syntax error . Try

This is, of course, nonsensical as mathematics, but it makes perfectly good sense as an assignment, with the right-hand side calculated first. Can you figure out the value that is now associated with width? Check by entering

In the assignment statement, the expression on the right is evaluated first . At that point width was associated with its original value 10, so width + 5 had the value of 10 + 5 which is 15. That value was then assigned to the variable on the left ( width again) to give it a new value. We will modify the value of variables in a similar way routinely.

Assignment and variables work equally well with strings. Try:

Try entering:

Note the different form of the error message. The earlier errors in these tutorials were syntax errors: errors in translation of the instruction. In this last case the syntax was legal, so the interpreter went on to execute the instruction. Only then did it find the error described. There are no quotes around fred , so the interpreter assumed fred was an identifier, but the name fred was not defined at the time the line was executed.

It is both easy to forget quotes where you need them for a literal string and to mistakenly put them around a variable name that should not have them!

Try in the Shell :

There fred , without the quotes, makes sense.

There are more subtleties to assignment and the idea of a variable being a “name for” a value, but we will worry about them later, in Issues with Mutable Objects . They do not come up if our variables are just numbers and strings.

Autocompletion: A handy short cut. Idle remembers all the variables you have defined at any moment. This is handy when editing. Without pressing Enter, type into the Shell just

Assuming you are following on the earlier variable entries to the Shell, you should see f autocompleted to be

This is particularly useful if you have long identifiers! You can press Alt-/ several times if more than one identifier starts with the initial sequence of characters you typed. If you press Alt-/ again you should see fred . Backspace and edit so you have fi , and then and press Alt-/ again. You should not see fred this time, since it does not start with fi .

1.6.1. Literals and Identifiers ¶

Expressions like 27 or 'hello' are called literals , coming from the fact that they literally mean exactly what they say. They are distinguished from variables, whose value is not directly determined by their name.

The sequence of characters used to form a variable name (and names for other Python entities later) is called an identifier . It identifies a Python variable or other entity.

There are some restrictions on the character sequence that make up an identifier:

The characters must all be letters, digits, or underscores _ , and must start with a letter. In particular, punctuation and blanks are not allowed.

There are some words that are reserved for special use in Python. You may not use these words as your own identifiers. They are easy to recognize in Idle, because they are automatically colored orange. For the curious, you may read the full list:

There are also identifiers that are automatically defined in Python, and that you could redefine, but you probably should not unless you really know what you are doing! When you start the editor, we will see how Idle uses color to help you know what identifies are predefined.

Python is case sensitive: The identifiers last , LAST , and LaSt are all different. Be sure to be consistent. Using the Alt-/ auto-completion shortcut in Idle helps ensure you are consistent.

What is legal is distinct from what is conventional or good practice or recommended. Meaningful names for variables are important for the humans who are looking at programs, understanding them, and revising them. That sometimes means you would like to use a name that is more than one word long, like price at opening , but blanks are illegal! One poor option is just leaving out the blanks, like priceatopening . Then it may be hard to figure out where words split. Two practical options are

• underscore separated: putting underscores (which are legal) in place of the blanks, like price_at_opening .
• using camel-case : omitting spaces and using all lowercase, except capitalizing all words after the first, like priceAtOpening

Use the choice that fits your taste (or the taste or convention of the people you are working with).

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Python Variables – A Guide to Variable Assignment and Naming

In Python, variables are essential elements that allow developers to store and manipulate data. When writing Python code, understanding variable assignment and naming conventions is crucial for effective programming.

Python variables provide a way to assign a name to a value and use that name to reference the value later in the code. Variables can be used to store various types of data, including numbers, strings, and lists.

In this article, we will explore the basics of Python variables, including variable assignment and naming conventions. We will also dive into the different variable types available in Python and how to use them effectively.

Key Takeaways

• Python variables are used to store and manipulate data in code.
• Variable assignment allows developers to assign a name to a value and reference it later.
• Proper variable naming conventions are essential for effective programming.
• Python supports different variable types, including integers, floats, strings, and lists.

Variable Assignment in Python

Python variables are created when a value is assigned to them using the equals sign (=) operator. For example, the following code snippet assigns the integer value 5 to the variable x :

From this point forward, whenever x is referenced in the code, it will have the value 5.

Variables can also be assigned using other variables or expressions. For example, the following code snippet assigns the value of x plus 2 to the variable y :

It is important to note that variables in Python are dynamically typed, meaning that their type can change as the program runs. For example, the following code snippet assigns a string value to the variable x , then later reassigns it to an integer value:

x = "hello" x = 7

Common Mistakes in Variable Assignment

One common mistake is trying to reference a variable before it has been assigned a value. This will result in a NameError being raised. For example:

print(variable_name) NameError: name ‘variable_name’ is not defined

Another common mistake is assigning a value to the wrong variable name. For example, the following code snippet assigns the value 5 to the variable y instead of x :

y = 5 print(x) NameError: name ‘x’ is not defined

To avoid these mistakes, it is important to carefully review code and double-check variable names and values.

Using Variables in Python

Variables are used extensively in Python code for a variety of purposes, from storing user input to performing complex calculations. The following code snippet demonstrates the basic usage of variables in a simple addition program:

number1 = input("Enter the first number: ") number2 = input("Enter the second number: ") sum = float(number1) + float(number2) print("The sum of", number1, "and", number2, "is", sum)

This program prompts the user to enter two numbers, converts them to floats using the float() function, adds them together, and prints the result using the print() function.

Variables can also be used in more complex operations, such as string concatenation and list manipulation. The following code snippet demonstrates how variables can be used to combine two strings:

greeting = "Hello" name = "Alice" message = greeting + ", " + name + "!" print(message)

This program defines two variables containing a greeting and a name, concatenates them using the plus (+) operator, and prints the result.

Variable Naming Conventions in Python

In Python, proper variable naming conventions are crucial for writing clear and maintainable code. Consistently following naming conventions makes code more readable and easier to understand, especially when working on large projects with many collaborators. Here are some commonly accepted conventions:

It’s recommended to use lowercase or snake case for variable names as they are easier to read and more commonly used in Python. Camel case is common in other programming languages, but can make Python code harder to read.

Variable names should be descriptive and meaningful. Avoid using abbreviations or single letters, unless they are commonly understood, like “i” for an iterative variable in a loop. Using descriptive names will make your code easier to understand and maintain by you and others.

Lastly, it’s a good practice to avoid naming variables with reserved words in Python such as “and”, “or”, and “not”. Using reserved words can cause errors in your code, making it hard to debug.

Scope of Variables in Python

Variables in Python have a scope, which dictates where they can be accessed and used within a code block. Understanding variable scope is important for writing efficient and effective code.

Local Variables in Python

A local variable is created within a particular code block, such as a function. It can only be accessed within that block and is destroyed when the block is exited. Local variables can be defined using the same Python variable assignment syntax as any other variable.

Example: def my_function():     x = 10     print(“Value inside function:”, x) my_function() print(“Value outside function:”, x) Output: Value inside function: 10 NameError: name ‘x’ is not defined

In the above example, the variable ‘x’ is a local variable that is defined within the function ‘my_function()’. It cannot be accessed outside of that function, which is why the second print statement results in an error.

Global Variables in Python

A global variable is a variable that can be accessed from anywhere within a program. These variables are typically defined outside of any code block, at the top level of the program. They can be accessed and modified from any code block within the program.

Example: x = 10 def my_function():     print(“Value inside function:”, x) my_function() print(“Value outside function:”, x) Output: Value inside function: 10 Value outside function: 10

In the above example, the variable ‘x’ is a global variable that is defined outside of any function. It can be accessed from within the ‘my_function()’ as well as from outside it.

When defining a function, it is possible to access and modify a global variable from within the function using the ‘global’ keyword.

Example: x = 10 def my_function():     global x     x = 20 my_function() print(x) Output: 20

In the above example, the ‘global’ keyword is used to indicate that the variable ‘x’ inside the function is the same as the global variable ‘x’. The function modifies the global variable, causing the final print statement to output ’20’ instead of ’10’.

One of the most fundamental concepts in programming is the use of variables. In Python, variables allow us to store and manipulate data efficiently. Here are some practical examples of how to use variables in Python:

Mathematical Calculations

Variables are often used to perform mathematical calculations in Python. For instance, we can assign numbers to variables and then perform operations on those variables. Here’s an example:

x = 5 y = 10 z = x + y print(z) # Output: 15

In this code, we have assigned the value 5 to the variable x and the value 10 to the variable y. We then create a new variable z by adding x and y together. Finally, we print the value of z, which is 15.

String Manipulation

Variables can also be used to manipulate strings in Python. Here is an example:

first_name = “John” last_name = “Doe” full_name = first_name + ” ” + last_name print(full_name) # Output: John Doe

In this code, we have assigned the strings “John” and “Doe” to the variables first_name and last_name respectively. We then create a new variable full_name by combining the values of first_name and last_name with a space in between. Finally, we print the value of full_name, which is “John Doe”.

Working with Data Structures

Variables are also essential when working with data structures such as lists and dictionaries in Python. Here’s an example:

numbers = [1, 2, 3, 4, 5] sum = 0 for num in numbers:     sum += num print(sum) # Output: 15

In this code, we have assigned a list of numbers to the variable numbers. We then create a new variable sum and initialize it to 0. We use a for loop to iterate over each number in the list, adding it to the sum variable. Finally, we print the value of sum, which is 15.

As you can see, variables are an essential tool in Python programming. By using them effectively, you can manipulate data and perform complex operations with ease.

Variable Types in Python

Python is a dynamically typed language, which means that variables can be assigned values of different types without explicit type declaration. Python supports a wide range of variable types, each with its own unique characteristics and uses.

Numeric Types:

Python supports several numeric types, including integers, floats, and complex numbers. Integers are whole numbers without decimal points, while floats are numbers with decimal points. Complex numbers consist of a real and imaginary part, expressed as a+bi.

Sequence Types:

Python supports several sequence types, including strings, lists, tuples, and range objects. Strings are sequences of characters, while lists and tuples are sequences of values of any type. Range objects are used to represent sequences of numbers.

Mapping Types:

Python supports mapping types, which are used to store key-value pairs. The most commonly used mapping type is the dictionary, which supports efficient lookup of values based on their associated keys.

Boolean Type:

Python supports a Boolean type, which is used to represent truth values. The Boolean type has two possible values: True and False.

Python has a special value called None, which represents the absence of a value. This type is often used to indicate the result of functions that do not return a value.

Understanding the different variable types available in Python is essential for effective coding. Each type has its own unique properties and uses, and choosing the right type for a given task can help improve code clarity, efficiency, and maintainability.

Python variables are a fundamental concept that every aspiring Python programmer must understand. In this article, we have covered the basics of variable assignment and naming conventions in Python. We have also explored the scope of variables and their different types.

It is important to remember that variables play a crucial role in programming, and their effective use can make your code more efficient and easier to read. Proper naming conventions and good coding practices can also help prevent errors and improve maintainability.

As you continue to explore the vast possibilities of Python programming, we encourage you to practice using variables in your code. With a solid understanding of Python variables, you will be well on your way to becoming a proficient Python programmer.

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Python is a widely used high-level programming language, loved by developers for its simplicity and code readability. One of the most important features that make Python stand out is its built-in data structures. These built-in data structures in Python are extremely useful when it comes to managing complex data. The Python collections module is a…

• Coding Fundamentals and Patterns

In this lesson, we will discuss the use of variables and assignment operators in Python, with a focus on the following key points:

• What are variables and the assignment of variables in the Python programming language?
• Working with variables and assignment of variables in an introductory programming language.

This is a general purpose tutorial for multiple languages. For the Javascript-specific version of this lesson that focuses on fundamentals frontend engineers need to know, please click here .

Throughout the day, we often need to store a piece of information somewhere and refer to it later.

We encounter these situations while writing a computer program as well, where we often need to store some information or data temporarily. For this specific purpose, variables are used. These variables can store almost any type of data, whether they are numbers, strings, or lists. Data is stored in variables by assign -ing data values to them. This lesson will expand on this topic and discuss variables and their assignment in detail.

As discussed above, variable s can store data. Data values can be assigned to a variable by using the assignment operator , which is the equal sign (=).

Once a value is assigned to the variable, it corresponds to that value unless it is re-assigned. Suppose we assign a value 5 to a variable a . This concept can be visualized as below.

This ensures that whenever we use the variable a in our program, we will get a value of 5. Let's understand this with code examples in Python.

Variables in Python

In Python, variables can be directly created by providing a variable name and assigning it some corresponding value. The code block below shows the creation of the variable number , which has the value 10 .

If we execute this code in a Python interpreter, it will give no output. Why?

Because this is a statement , and this statement did not tell the programming language to display the value of variable number . For that, we'd need to either print() it, or log it out in some other way.

However, it did create a variable number in memory and assigned it the value 10 . To check if the value was properly assigned, type either the variable name on the console, or use the print() function. It will display the variable name on the console.

The value that you stored earlier in number is successfully displayed, and we can see that it correctly assigned the value.

Important Rules while Creating Variables

Programming languages understand instructions only if they are given in a specified format (or syntax). When creating variables, we need to be careful of these rules, or the variables will not be created properly, and the program may give errors.

• Variable names can be created using alphabetical letters (a-z and A-Z), digits (0-9), or underscore symbol (_). Special symbols are not allowed. For example, abc&def is an invalid variable name.
• Variable names can begin with the underscore symbol or alphabetical letters only, not digits. For example, 123abc is an invalid variable name and will give you an error.
• Variables in Python are case-sensitive . This means that if we declare two variables score and Score with different values assigned to them, then they are two different variables (not the same variable!).
• Every programming language has certain keywords , that define in-built functionality in the language. These should not be used as variable names. Since it has a different meaning in the language, declaring variables with already existing keyword names will cause an error. These keywords will be highlighted with a different color whenever you type them, so it is easy for you to distinguish. For example, and is a keyword in Python, hence declaring a variable with that name would raise an error.
• In Python, it is important to assign a value to a variable. If you only define the variable without assigning it a value, it will produce an error.

Now that we know how to create variables, let's see if we understood them properly.

Are you sure you're getting this? Is this statement true or false?

Is the following code snippet a valid way to declare a variable?

Press true if you believe the statement is correct, or false otherwise.

Let's test your knowledge. Is this statement true or false?

Is _name a valid variable name?

Reassigning variables

Values can be reassigned to variables in Python. When variables are reassigned, their value changes to that of the newer value specified, and the previous value is lost.

Let's look at an example. We can reassign variable values in Python as follows.

The reassignment works similarly to how we create the variable. We only provide a different value than what was stored before. Here, the initial value of a was 10 , which was reassigned to 20 from the second line in the above code block.

Operations on Variables

Using variables in the program makes it easy for us to perform various operations on data. Different types of variables support different types of operations. For simplicity, let's consider the type integer. On this type of variable, all mathematical operations are valid.

Let's understand this with a code example.

This code block shows that if we have two integer variables, we can add them and get the result. Similarly, other mathematical operations such as subtraction, multiplication, and division are also supported.

Now let's consider if we have a variable of type string. In this case, the operations are defined differently. Here, a + symbol between two variables will join the two strings together.

Here, the two strings are joined together to produce a new string. This operation is called concatenation . There are several other operations that we can perform on strings, integers, and other types of variables, but we will discuss them in later lessons.

Time for some practice questions!

Are you sure you're getting this? Fill in the missing part by typing it in.

What will be the final value of variable a below?

Write the missing line below.

Are you sure you're getting this? Click the correct answer from the options.

What will the following program output?

Click the option that best answers the question.

• Will give an error

In this lesson, we talked about a basic concept in programming, about the creation of variables and assigning values to them. A useful tip for creating variables is to use meaningful names while creating them. If you have a lot of variables in your program and you don't name them properly, there is a high chance that you'll get confused about which variables were supposed to store what value!

One Pager Cheat Sheet

• This lesson will discuss variables and assignment of data values in Python for storing data temporarily.
• Variables are placeholders for data values that can be assigned using the assignment operator (=) and re-assigned when needed.
• Python can create variables directly by providing a name and assigning it a value, as shown in the code blocks, and then use the print() or variable name to display the stored value.
• We need to be careful to follow the specific syntax rules when creating variables, or they may not be created correctly and cause errors.
• Creating a variable in Python is done by having a variable name followed by an assignment operator (=) and a value , as is the case with the code snippet words = "Hello World!" , which is a valid way to declare the variable words .
• Yes, using an underscore (_) is a valid way to name variables in Python.
• Variables can be reassigned in Python, replacing their previous value with a newer one .
• We can perform different operations on each type of variable, such as mathematical operations on integers or concatenation of strings.
• The final value of a is "World" .
• The program prints the result of concatenating the values in the first_name and last_name variables, which is AnnaGreen .
• Creating meaningful variable names is key to being able to keep track of values stored in a program .

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CS101: Introduction to Computer Science I

Variables and Assignment Statements

Read this chapter, which covers variables and arithmetic operations and order precedence in Java.

5. Syntax of Variable Declaration

Syntax of variable deceleration.

The word  syntax  means the grammar of a programming language. We can talk about the syntax of just a small part of a program, such as the syntax of variable declaration.

There are several ways to declare variables:

• This declares a variable, declares its data type, and reserves memory for it. It says nothing about what value is put in memory. (Later in these notes you will learn that in some circumstances the variable is automatically initialized, and that in other circumstances the variable is left uninitialized.)
• This declares a variable, declares its data type, reserves memory for it, and puts an initial value into that memory. The initial value must be of the correct data type.
• This declares  two  variables, both of the same data type, reserves memory for each, but puts nothing in any variable. You can do this with more than two variables, if you want.
• This declares  two  variables, both of the same data type, reserves memory, and puts an initial value in each variable. You can do this all on one line if there is room. Again, you can do this for more than two variables as long as you follow the pattern.

If you have several variables of different types, use several declaration statements. You can even use several declaration statements for several variables of the same type.

Question 4:

Is the following correct?

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Home Assignment and Initialization

Assignment and Initialization

Assignment and initialization are fundamental concepts in programming languages that involve storing values in variables. While they may seem similar, they serve different purposes and have distinct roles in programming.

Assignment:

Assignment is the process of giving a value to a variable. It involves storing a specific value or the result of an expression in a named memory location, which is the variable. The assignment operator, usually represented by the equal sign (=), is used to perform this operation.

Example in Python:

In this example, the value 10 is assigned to the variable ‘x’. After the assignment, ‘x’ holds the value 10.

Assignment is a common operation used to update the value of variables during program execution. It allows variables to store and represent changing data, making programs more dynamic and versatile.

Initialization:

Initialization is the process of setting a variable to a known value when it is first created. It ensures that the variable has a valid and predictable starting value before any further operations are performed on it.

Example in C++:

In this example, the variable ‘count’ is initialized to 0 when it is declared. This ensures that the variable has a specific starting value before any other operations use it.

Initialization is essential for avoiding unpredictable behavior and bugs caused by using variables with undefined values. Many programming languages enforce initialization of variables to prevent potential issues and improve code reliability.

Differences and Use Cases:

The key difference between assignment and initialization lies in their timing and purpose:

• Assignment occurs after a variable is declared and provides a value to an existing variable.
• Initialization happens at the time of variable declaration and sets a starting value for the variable.
• Assignment: Assigning new values to variables during program execution, updating data as it changes, and performing calculations using variable values.
• Initialization: Setting variables to predefined starting values, ensuring variables are valid before use, and initializing data structures to default values.

Combination of Assignment and Initialization:

In many cases, assignment and initialization are combined when declaring variables. The variable is declared and assigned an initial value in a single statement.

Example in Java:

In this example, the variable ‘age’ is both declared and initialized with the value 25.

Importance and Best Practices:

Proper assignment and initialization of variables are critical for writing bug-free and maintainable code. Uninitialized variables can lead to undefined behavior and unexpected results, while incorrect assignments can produce incorrect calculations or data processing.

To ensure code reliability and readability, developers should:

• Initialize variables at the time of declaration, whenever possible, to avoid using variables with undefined values.
• Double-check assignment statements to ensure that the correct value is being assigned to the appropriate variable.
• Use meaningful variable names to improve code understanding and maintainability.
• Avoid reusing variables for different purposes to reduce confusion and potential bugs.

Numeric Data Types

Assignment and initialization of numeric data types involve storing numerical values in variables. Assignment is the process of assigning a specific value to a variable after its declaration, allowing the variable to hold and represent changing numerical data during program execution. Initialization, on the other hand, sets a starting value for the variable at the time of declaration, ensuring it has a valid value before any further operations. Numeric data types, such as integers and floating-point numbers, are commonly used for arithmetic calculations and numerical processing in programming. Proper assignment and initialization of numeric data types are essential for accurate calculations and data manipulation in programs.

Enumerations

Assignment and initialization of enumerations involve defining and setting values for user-defined data types that represent a set of named constant values. Enumerations are typically used to improve code readability and maintainability by providing meaningful names for specific values. Assignment in enumerations assigns specific constant values to the defined identifiers, allowing them to be used throughout the program. Initialization of enumerations is often done implicitly when the program starts, ensuring that the enumeration is ready for use. Enumerations are powerful tools for organizing related constants and simplifying code, making them an important aspect of many programming languages.

Assignment and initialization of Booleans involve working with a data type that represents logical values, typically denoted as “true” or “false.” Assignment assigns a Boolean value to a variable after its declaration, allowing the variable to hold and represent changing truth values during program execution. Initialization, on the other hand, sets a starting Boolean value for the variable at the time of declaration, ensuring it has a valid truth value before any further operations. Booleans are fundamental in decision-making, conditionals, and control flow in programming. Proper assignment and initialization of Booleans are crucial for implementing logic-based algorithms and ensuring the accuracy of conditional statements in programs.

Assignment and initialization of characters involve working with a data type that represents individual symbols from the character set, such as letters, digits, and special symbols. Assignment assigns a specific character to a variable after its declaration, allowing the variable to hold and represent changing characters during program execution. Initialization, on the other hand, sets a starting character value for the variable at the time of declaration, ensuring it has a valid character value before any further operations. Characters are commonly used for text processing, input/output operations, and string manipulation in programming. Proper assignment and initialization of characters are essential for handling textual data accurately and effectively in programs.

more related content on  Principles of Programming Languages

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Assignment operator in python.

Last Updated on June 8, 2023 by Prepbytes

To fully comprehend the assignment operators in Python, it is important to have a basic understanding of what operators are. Operators are utilized to carry out a variety of operations, including mathematical, bitwise, and logical operations, among others, by connecting operands. Operands are the values that are acted upon by operators. In Python, the assignment operator is used to assign a value to a variable. The assignment operator is represented by the equals sign (=), and it is the most commonly used operator in Python. In this article, we will explore the assignment operator in Python, how it works, and its different types.

What is an Assignment Operator in Python?

The assignment operator in Python is used to assign a value to a variable. The assignment operator is represented by the equals sign (=), and it is used to assign a value to a variable. When an assignment operator is used, the value on the right-hand side is assigned to the variable on the left-hand side. This is a fundamental operation in programming, as it allows developers to store data in variables that can be used throughout their code.

For example, consider the following line of code:

Explanation: In this case, the value 10 is assigned to the variable a using the assignment operator. The variable a now holds the value 10, and this value can be used in other parts of the code. This simple example illustrates the basic usage and importance of assignment operators in Python programming.

Types of Assignment Operator in Python

There are several types of assignment operator in Python that are used to perform different operations. Let’s explore each type of assignment operator in Python in detail with the help of some code examples.

1. Simple Assignment Operator (=)

The simple assignment operator is the most commonly used operator in Python. It is used to assign a value to a variable. The syntax for the simple assignment operator is:

Here, the value on the right-hand side of the equals sign is assigned to the variable on the left-hand side. For example

Explanation: In this case, the value 25 is assigned to the variable a using the simple assignment operator. The variable a now holds the value 25.

2. Addition Assignment Operator (+=)

The addition assignment operator is used to add a value to a variable and store the result in the same variable. The syntax for the addition assignment operator is:

Here, the value on the right-hand side is added to the variable on the left-hand side, and the result is stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is incremented by 5 using the addition assignment operator. The result, 15, is then printed to the console.

3. Subtraction Assignment Operator (-=)

The subtraction assignment operator is used to subtract a value from a variable and store the result in the same variable. The syntax for the subtraction assignment operator is

Here, the value on the right-hand side is subtracted from the variable on the left-hand side, and the result is stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is decremented by 5 using the subtraction assignment operator. The result, 5, is then printed to the console.

4. Multiplication Assignment Operator (*=)

The multiplication assignment operator is used to multiply a variable by a value and store the result in the same variable. The syntax for the multiplication assignment operator is:

Here, the value on the right-hand side is multiplied by the variable on the left-hand side, and the result is stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is multiplied by 5 using the multiplication assignment operator. The result, 50, is then printed to the console.

5. Division Assignment Operator (/=)

The division assignment operator is used to divide a variable by a value and store the result in the same variable. The syntax for the division assignment operator is:

Here, the variable on the left-hand side is divided by the value on the right-hand side, and the result is stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is divided by 5 using the division assignment operator. The result, 2.0, is then printed to the console.

6. Modulus Assignment Operator (%=)

The modulus assignment operator is used to find the remainder of the division of a variable by a value and store the result in the same variable. The syntax for the modulus assignment operator is

Here, the variable on the left-hand side is divided by the value on the right-hand side, and the remainder is stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is divided by 3 using the modulus assignment operator. The remainder, 1, is then printed to the console.

7. Floor Division Assignment Operator (//=)

The floor division assignment operator is used to divide a variable by a value and round the result down to the nearest integer, and store the result in the same variable. The syntax for the floor division assignment operator is:

Here, the variable on the left-hand side is divided by the value on the right-hand side, and the result is rounded down to the nearest integer. The rounded result is then stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is divided by 3 using the floor division assignment operator. The result, 3, is then printed to the console.

8. Exponentiation Assignment Operator (**=)

The exponentiation assignment operator is used to raise a variable to the power of a value and store the result in the same variable. The syntax for the exponentiation assignment operator is:

Here, the variable on the left-hand side is raised to the power of the value on the right-hand side, and the result is stored back in the variable on the left-hand side. For example

Explanation: In this case, the value of a is raised to the power of 3 using the exponentiation assignment operator. The result, 8, is then printed to the console.

9. Bitwise AND Assignment Operator (&=)

The bitwise AND assignment operator is used to perform a bitwise AND operation on the binary representation of a variable and a value, and store the result in the same variable. The syntax for the bitwise AND assignment operator is:

Here, the variable on the left-hand side is ANDed with the value on the right-hand side using the bitwise AND operator, and the result is stored back in the variable on the left-hand side. For example,

Explanation: In this case, the value of a is ANDed with 3 using the bitwise AND assignment operator. The result, 2, is then printed to the console.

10. Bitwise OR Assignment Operator (|=)

The bitwise OR assignment operator is used to perform a bitwise OR operation on the binary representation of a variable and a value, and store the result in the same variable. The syntax for the bitwise OR assignment operator is:

Here, the variable on the left-hand side is ORed with the value on the right-hand side using the bitwise OR operator, and the result is stored back in the variable on the left-hand side. For example,

Explanation: In this case, the value of a is ORed with 3 using the bitwise OR assignment operator. The result, 7, is then printed to the console.

11. Bitwise XOR Assignment Operator (^=)

The bitwise XOR assignment operator is used to perform a bitwise XOR operation on the binary representation of a variable and a value, and store the result in the same variable. The syntax for the bitwise XOR assignment operator is:

Here, the variable on the left-hand side is XORed with the value on the right-hand side using the bitwise XOR operator, and the result are stored back in the variable on the left-hand side. For example,

Explanation: In this case, the value of a is XORed with 3 using the bitwise XOR assignment operator. The result, 5, is then printed to the console.

12. Bitwise Right Shift Assignment Operator (>>=)

The bitwise right shift assignment operator is used to shift the bits of a variable to the right by a specified number of positions, and store the result in the same variable. The syntax for the bitwise right shift assignment operator is:

Here, the variable on the left-hand side has its bits shifted to the right by the number of positions specified by the value on the right-hand side, and the result is stored back in the variable on the left-hand side. For example,

Explanation: In this case, the value of a is shifted 2 positions to the right using the bitwise right shift assignment operator. The result, 2, is then printed to the console.

13. Bitwise Left Shift Assignment Operator (<<=)

The bitwise left shift assignment operator is used to shift the bits of a variable to the left by a specified number of positions, and store the result in the same variable. The syntax for the bitwise left shift assignment operator is:

Here, the variable on the left-hand side has its bits shifted to the left by the number of positions specified by the value on the right-hand side, and the result is stored back in the variable on the left-hand side. For example,

Conclusion Assignment operator in Python is used to assign values to variables, and it comes in different types. The simple assignment operator (=) assigns a value to a variable. The augmented assignment operators (+=, -=, *=, /=, %=, &=, |=, ^=, >>=, <<=) perform a specified operation and assign the result to the same variable in one step. The modulus assignment operator (%) calculates the remainder of a division operation and assigns the result to the same variable. The bitwise assignment operators (&=, |=, ^=, >>=, <<=) perform bitwise operations and assign the result to the same variable. The bitwise right shift assignment operator (>>=) shifts the bits of a variable to the right by a specified number of positions and stores the result in the same variable. The bitwise left shift assignment operator (<<=) shifts the bits of a variable to the left by a specified number of positions and stores the result in the same variable. These operators are useful in simplifying and shortening code that involves assigning and manipulating values in a single step.

Here are some Frequently Asked Questions on Assignment Operator in Python:

Q1 – Can I use the assignment operator to assign multiple values to multiple variables at once? Ans – Yes, you can use the assignment operator to assign multiple values to multiple variables at once, separated by commas. For example, "x, y, z = 1, 2, 3" would assign the value 1 to x, 2 to y, and 3 to z.

Q2 – Is it possible to chain assignment operators in Python? Ans – Yes, you can chain assignment operators in Python to perform multiple operations in one line of code. For example, "x = y = z = 1" would assign the value 1 to all three variables.

Q3 – How do I perform a conditional assignment in Python? Ans – To perform a conditional assignment in Python, you can use the ternary operator. For example, "x = a (if a > b) else b" would assign the value of a to x if a is greater than b, otherwise it would assign the value of b to x.

Q4 – What happens if I use an undefined variable in an assignment operation in Python? Ans – If you use an undefined variable in an assignment operation in Python, you will get a NameError. Make sure you have defined the variable before trying to assign a value to it.

Q5 – Can I use assignment operators with non-numeric data types in Python? Ans – Yes, you can use assignment operators with non-numeric data types in Python, such as strings or lists. For example, "my_list += [4, 5, 6]" would append the values 4, 5, and 6 to the end of the list named my_list.

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Assignment (=)

The assignment ( = ) operator is used to assign a value to a variable or property. The assignment expression itself has a value, which is the assigned value. This allows multiple assignments to be chained in order to assign a single value to multiple variables.

A valid assignment target, including an identifier or a property accessor . It can also be a destructuring assignment pattern .

An expression specifying the value to be assigned to x .

Return value

The value of y .

Thrown in strict mode if assigning to an identifier that is not declared in the scope.

Thrown in strict mode if assigning to a property that is not modifiable .

Description

The assignment operator is completely different from the equals ( = ) sign used as syntactic separators in other locations, which include:

• Initializers of var , let , and const declarations
• Default values of destructuring
• Default parameters
• Initializers of class fields

All these places accept an assignment expression on the right-hand side of the = , so if you have multiple equals signs chained together:

This is equivalent to:

Which means y must be a pre-existing variable, and x is a newly declared const variable. y is assigned the value 5 , and x is initialized with the value of the y = 5 expression, which is also 5 . If y is not a pre-existing variable, a global variable y is implicitly created in non-strict mode , or a ReferenceError is thrown in strict mode. To declare two variables within the same declaration, use:

Simple assignment and chaining

Value of assignment expressions.

The assignment expression itself evaluates to the value of the right-hand side, so you can log the value and assign to a variable at the same time.

Unqualified identifier assignment

The global object sits at the top of the scope chain. When attempting to resolve a name to a value, the scope chain is searched. This means that properties on the global object are conveniently visible from every scope, without having to qualify the names with globalThis. or window. or global. .

Because the global object has a String property ( Object.hasOwn(globalThis, "String") ), you can use the following code:

So the global object will ultimately be searched for unqualified identifiers. You don't have to type globalThis.String ; you can just type the unqualified String . To make this feature more conceptually consistent, assignment to unqualified identifiers will assume you want to create a property with that name on the global object (with globalThis. omitted), if there is no variable of the same name declared in the scope chain.

In strict mode , assignment to an unqualified identifier in strict mode will result in a ReferenceError , to avoid the accidental creation of properties on the global object.

Note that the implication of the above is that, contrary to popular misinformation, JavaScript does not have implicit or undeclared variables. It just conflates the global object with the global scope and allows omitting the global object qualifier during property creation.

Assignment with destructuring

The left-hand side of can also be an assignment pattern. This allows assigning to multiple variables at once.

For more information, see Destructuring assignment .

Specifications

Browser compatibility.

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

• Assignment operators in the JS guide
• Destructuring assignment

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Scope of a variable

Scope of a variable defines the part of code where the variable can be accessed or modified. It helps in organizing code by limiting where variables are available, preventing unintended changes or conflicts. Understanding scope is key to writing clear, efficient, and maintainable programs. In this article, we will cover the basics of Scope of a variable, types of Scope in different languages, its importance, etc.

What is Scope of a Variable?

Scope of a variable defines the region of the code where a particular variable can be referenced or used. Scope holds the current state of variables along with their respective values. Scope of a variable is depends on where the value is declared in the program. Once, a variable is declared, we can access and manipulate its data according to our needs. Understanding how the variable’s value is accessed and used within its scope is essential to find out the program’s behavior.

Once the program exits the scope where a variable is defined, the memory allocated to that variable is usually released, making the variable inaccessible. This ensures that resources are efficiently managed and prevents accidental access or modification of the variable’s data outside its intended scope.

Scope of a variable in different programming languages

1. scope of a variable in c.

Variables in C can have two types of scopes:

• Local Scope or Block Scope: The variables declared within the local scope are called local variables. Local variables are visible in the block they are declared in and other blocks nested inside that block.
• Global Scope or File Scope : The variables declared in the global scope are called global variables. Global variables are visible in every part of the program.

Below is the implementation of different types of Scopes in C:

2. Scope of a variable in C++

Similar to C, Variables in C++ can have two types of scopes:

• Global Scope or File Scope: The variables declared in the global scope are called global variables. Global variables are visible in every part of the program.

Below is the implementation of different types of Scopes in C++:

3. Scope of a variable in Java

Variables in Java can have three types of scopes:

• Class Scope: The variables declared in the class with private access modifier but outside the methods, have class scope. Class Scoped variables can be used anywhere inside the class but not outside it.
• Block Scope: The variables declared inside a block, wrapped in a pair of curly braces {} have block scope. Block scoped variables can be accessed anywhere inside the block but not outside it.

Below is the implementation of different types of Scopes in Java:

4. Scope of a variable in Python

• Local Scope: In Python, variables are usually limited to where they are created, such as inside functions, loops, or blocks of code. These are called local variables.
• Global Scope: Global variables are the ones that are defined and declared outside any function and are not specified to any function. They can be used by any part of the program.

Below is the implementation of different types of Scopes in Python:

5. Scope of a variable in C#

Variables in C# can have two types of scopes:

• Class Scope: The variables declared inside the class but outside any method are called class variables.

Below is the implementation of different types of Scopes in C#:

6. Scope of a variable in JavaScript

Variables in JavaScript can have two types of scopes:

• Block Scope: Block scope was introduced in ES6(2015). The variables declared inside a block, wrapped in a pair of curly braces {} have block scope. Block scoped variables can be accessed anywhere inside the block but not outside it. let and const are block scoped whereas var is global scoped.
• Global Scope: The variables declared outside any function or block have Global scope .
• Function Scope: The variables declared inside any function is called function scoped. In Javascript, each function creates a new scope. The variables declared inside a function (var, let or const) cannot be accessed outside the function.

Below is the implementation of different types of Scopes in JavaScript:

Importance of Scope of a Variable:

Below is the importance of Scope of a variable:

• Prevents Differences in Naming: It can be limited variable’s visibility to specific areas of your code prevents confusion and errors that arise from using the same name for different variables in different parts of your program. This practice ensures clarity and helps maintain code reliability and readability.
• More Effective Organization of Code: Scope in programming specifies where variables can be accessed and used, ensuring a structured and organized codebase. By defining clear boundaries, scope enhances readability and makes it easier to manage and update code. It prevents conflicts and confusion by limiting variable access to specific parts of the program, promoting efficient development and maintenance practices.
• Reduced Risk of Unintended Modifications : Local variables safeguard data integrity by confining changes solely to their designated part of the program. This prevents unintentional alterations from affecting other areas, enhancing the reliability and stability of the data.

Advantages of Defining Scope:

• Promotes Code Clarity: Scope sets rules for where values can be used in code, making it easy to understand. It keeps things organized so developers can work with the code without confusion. This clarity helps in maintaining and fixing code, making it easier to manage in the long run.
• Minimizes Errors : Scope in coding keeps things organized by setting clear rules on where variables can be used. This prevents mix-ups and errors that can occur when using the same names for different things in different parts of the program. It makes coding smoother and less prone to mistakes.
• Enhances Maintainability: Scoped variables simplify code editing by indicating where to make changes without impacting other areas. They maintain clarity and prevent confusion by confining variable usage to specific parts of code, highlighting which sections require modification. This focused approach streamlines the process of updating and maintaining code.

Where variables can be used, making debugging simpler and reducing the risk of errors caused by naming conflicts. By carefully managing variable visibility and lifespan, you ensure that your code runs smoothly and efficiently. Choosing appropriate scope levels and giving variables meaningful names are essential practices for developing robust and maintainable programs.

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Column assignment and reference semantics in {data.table}.

Posted on February 18, 2024 by Toby Hocking in R bloggers | 0 Comments

The goal of this blog post is to explain some similarities and differences between the base R data.frame object type, and the data.table object type. We will focus on accessing and assigning values, and discuss two major differences:

Syntax means the structure of the code that is used: the characters and symbols that execute tasks. The data.table package uses a syntax where most operations can be done within the square brackets: DT[i, j, by] .

Semantics refers to the internal structure of an object or variable. We say that a data.table object has reference semantics , meaning we can modify a data.table from within a function, and see those modifications after the function is done executing. In other words, two different R variables can point to, and modify, the same data.table .

Difference in syntax

To break down the similarities and differences in syntax, consider the data below,

The table above defines the different syntax required to do column assignment in data tables ( DT ) and frames ( df ).

type indicates object type: frame or table .

name indicates whether the column(s) to assign are literally written in the code ( col_name ), or if the names are stored in a variable ( col_names_list ).

columns indicates whether only one or multiple (one or more) columns can be assigned using the syntax.

code is the exact syntax of the R code used for the assignment.

Note that there are other ways to do column assignment. For example,

DF[["col_name"]] <- value can also be used for single column assignment in a data frame.

set(DT, j=col_name_list, value=values) is a more efficient version of column assignment for data tables, that is recommended for use in loops, as it avoids the overhead of the [.data.table method.

Below is a reshaped version of the table above, to facilitate easier comparison between frame and table versions:

The table above shows the equivalent code for assignment of columns using either a data.frame or data.table . In fact, the code in the frame column above can also be used for assignment of a data.table , but it may be less efficient than the data table square brackets, as we will discuss in the next section.

One reason why data.table uses a custom assignment syntax is for consistency: the same syntax can be used, with square brackets and := , for one or multiple column assignment. (Note the use parentheses around col_names_list in the second row of the table column above, to indicate that the left side of := is a variable storing column names or numbers, instead of a direct unquoted column name.)

Another reason why data.table uses a custom assignment syntax is for efficiency, as we see in the next section.

Base “copy on write” versus data.table reference semantics

R has “copy on write” semantics, meaning that in base R if a variable is modified inside a function, a copy is made of the whole variable. For example, consider the code below

In the code above, we pass dt_outside to the base_assign function, which makes a copy called dt_inside before it is modified, so that the data in dt_outside is unchanged after the function is done. Compare with the code below,

The output above shows that by using the square brackets and := assignment, we can modify data.table objects in functions without copying them. Here, the variables dt_inside and dt_outside point to the same underlying data.

Efficiency of reference semantics

The code in this section used a data.table object in both function calls to illustrate the constant time/space assignment which is possible, but the visualized result also applies to other data structures.

As an exercise, add two more expressions to the atime benchmark: base_assign with a data.frame object and tibble object. You should see linear time/space for both.

Conclusions

In this post we have explored the syntax and semantics for assignment using base R and data.table square brackets with := , and we have seen how the reference semantics of data.table can be very beneficial for computational efficiency.

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