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Python 101 – Assignment Expressions

Assignment expressions were added to Python in version 3.8 . The general idea is that an assignment expression allows you to assign to variables within an expression.

The syntax for doing this is:

This operator has been called the “walrus operator”, although their real name is “assignment expression”. Interestingly, the CPython internals also refer to them as “named expressions”.

You can read all about assignment expressions in PEP 572 . Let’s find out how to use assignment expressions!

Using Assignment Expressions

Assignment expressions are still relatively rare. However, you need to know about assignment expressions because you will probably come across them from time to time. PEP 572 has some good examples of assignment expressions.

In these 3 examples, you are creating a variable in the expression statement itself. The first example creates the variable match by assigning it the result of the regex pattern search. The second example assigns the variable value to the result of calling a function in the while loop’s expression. Finally, you assign the result of calling f(x) to the variable y inside of a list comprehension.

It would probably help to see the difference between code that doesn’t use an assignment expression and one that does. Here’s an example of reading a file in chunks:

This code will open up a file of indeterminate size and process it 1024 bytes at a time. You will find this useful when working with very large files as it prevents you from loading the entire file into memory. If you do, you can run out of memory and cause your application or even the computer to crash.

You can shorten this code up a bit by using an assignment expression:

Here you assign the result of the read() to data within the while loop’s expression. This allows you to then use that variable inside of the while loop’s code block. It also checks that some data was returned so you don’t have to have the if not data: break stanza.

Another good example that is mentioned in PEP 572 is taken from Python’s own site.py . Here’s how the code was originally:

And this is how it could be simplified by using an assignment expression:

You move the assignment into the conditional statement’s expression, which shortens the code up nicely.

Now let’s discover some of the situations where assignment expressions can’t be used.

What You Cannot Do With Assignment Expressions

There are several cases where assignment expressions cannot be used.

One of the most interesting features of assignment expressions is that they can be used in contexts that an assignment statement cannot, such as in a lambda or the previously mentioned comprehension. However, they do NOT support some things that assignment statements can do. For example, you cannot do multiple target assignment:

Another prohibited use case is using an assignment expression at the top level of an expression statement. Here is an example from PEP 572:

There is a detailed list of other cases where assignment expressions are prohibited or discouraged in the PEP. You should check that document out if you plan to use assignment expressions often.

Wrapping Up

Assignment expressions are an elegant way to clean up certain parts of your code. The feature’s syntax is kind of similar to type hinting a variable. Once you have the hang of one, the other should become easier to do as well.

In this article, you saw some real-world examples of using the “walrus operator”. You also learned when assignment expressions shouldn’t be used. This syntax is only available in Python 3.8 or newer, so if you happen to be forced to use an older version of Python, this feature won’t be of much use to you.

Related Reading

This article is based on a chapter from Python 101, 2nd Edition , which you can purchase on Leanpub or Amazon .

If you’d like to learn more Python, then check out these tutorials:

Python 101 – How to Work with Images

Python 101 – Documenting Your Code

Python 101: An Intro to Working with JSON

Python 101 – Creating Multiple Processes

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Support Assignment Expression ("walrus" operator) syntax #8530

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bcoov commented Nov 12, 2019

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Bcoov commented nov 14, 2019, karthiknadig commented nov 14, 2019, bcoov commented nov 15, 2019, karthiknadig commented nov 19, 2019.

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Python Enhancement Proposals

  • Python »
  • PEP Index »

PEP 379 – Adding an Assignment Expression

Motivation and summary, specification, examples from the standard library.

This PEP adds a new assignment expression to the Python language to make it possible to assign the result of an expression in almost any place. The new expression will allow the assignment of the result of an expression at first use (in a comparison for example).

Issue1714448 “if something as x:” [1] describes a feature to allow assignment of the result of an expression in an if statement to a name. It supposed that the as syntax could be borrowed for this purpose. Many times it is not the expression itself that is interesting, rather one of the terms that make up the expression. To be clear, something like this:

seems awfully limited, when this:

is probably the desired result.

See the Examples section near the end.

A new expression is proposed with the (nominal) syntax:

This single expression does the following:

  • Evaluate the value of EXPR , an arbitrary expression;
  • Assign the result to VAR , a single assignment target; and
  • Leave the result of EXPR on the Top of Stack (TOS)

Here -> or ( RARROW ) has been used to illustrate the concept that the result of EXPR is assigned to VAR .

The translation of the proposed syntax is:

The assignment target can be either an attribute, a subscript or name:

This expression should be available anywhere that an expression is currently accepted.

All exceptions that are currently raised during invalid assignments will continue to be raised when using the assignment expression. For example, a NameError will be raised when in example 1 and 2 above if name is not previously defined, or an IndexError if index 0 was out of range.

The following two examples were chosen after a brief search through the standard library, specifically both are from ast.py which happened to be open at the time of the search.

Using assignment expression:

The examples shown below highlight some of the desirable features of the assignment expression, and some of the possible corner cases.

  • Assignment in an if statement for use later: def expensive (): import time ; time . sleep ( 1 ) return 'spam' if expensive () -> res in ( 'spam' , 'eggs' ): dosomething ( res )
  • Assignment in a while loop clause: while len ( expensive () -> res ) == 4 : dosomething ( res )
  • Keep the iterator object from the for loop: for ch in expensive () -> res : sell_on_internet ( res )
  • Corner case: for ch -> please_dont in expensive (): pass # who would want to do this? Not I.

This document has been placed in the public domain.

Source: https://github.com/python/peps/blob/main/peps/pep-0379.rst

Last modified: 2023-09-09 17:39:29 GMT

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[Solved] SyntaxError: cannot assign to expression here in Python

Python raises “SyntaxError: cannot assign to expression here. Maybe you meant ‘==’ instead of ‘=’?” when you assign a value to an expression. On the other hand, this error occurs if an expression is the left-hand side operand in an assignment statement.

Additionally, Python provides you a hint, assuming you meant to use the equality operator ( == ):

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But what's a expression? You may ask. 

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The term "expression" refers to values or combination of values (operands) and operators that result in a value. That said, all the following items are expressions:

  • 'someValue'
  • 4 * (5 + 2)
  • 'someText' + 'anotherText'

Most of the time, the cause of the "SyntaxError: cannot assign to expression here" error is a typo in your code - usually a missing = or invalid identifiers in assignment statements.

How to fix "SyntaxError: cannot assign to expression here"

The long error "SyntaxError: cannot assign to expression here. Maybe you meant '==' instead of '='?" occurs under various scenarios:

  • Using an invalid name (identifier) in an assignment statement
  • Using = instead of == in a comparison statement

Let's see some examples.

Using an invalid name (identifier) in an assignment statement:  Assignment statements bind names to values. (e.g., total_price = 49.99 )

 Based on Python syntax and semantics , the left-hand side of the assignment operator ( = ) should always be an identifier, not an expression or a literal.

Identifiers (a.k.a names) are arbitrary names you use for definitions in the source code, such as variable names, function names, and class names. For instance, in the statement age = 25 , age is the identifier.

Python identifiers  are based on the  Unicode standard annex UAX-31 , which describes the specifications for using Unicode in identifiers.

That said, you can only use alphanumeric characters and underscores for names. Otherwise, you'll get a SyntaxError. For instance, 2 + 2 = a is a syntax error because the left-hand side operator isn't a valid identifier - it's a Python expression.

A common mistake which results in the "SyntaxError: cannot assign to expression here. Maybe you meant '==' instead of '='?" error is using hyphens ( - ) in your variable names.

Hyphens are only valid in expressions like 45.54 - 12.12 . If you have a '-' in your variable name, Python's interpreter would assume it's an expression:

In the above code, Python's interpreter assumes you're trying to subtract a variable name price from another variable named total .

And since you can't have an expression as a left-hand side operand in an assignment statement, you'll get this SyntaxError.

So if your code looks like the above, you need to replace the hyphen ( - ) with an underscore ( _ ):

That's much better!

Invalid comparison statement :  Another cause of "SyntaxError: cannot assign to expression here" is using an invalid sequence of comparison operators while comparing values .

This one is more of a syntax-related mistake and rarely finds its way to the runtime, but it's worth watching.

Imagine you want to test if a number is an even number. As you probably know, if we divide a number by 2 , and the remainder is 0 , that number is even.

In Python, we use the modulo operator ( % ) to get the remainder of a division:

In the above code, once Python encounters the assignment operator ( = ), it assumes we're trying to assign 0 to x % 2 ! No wonder the response is "SyntaxError: cannot assign to expression here. Maybe you meant '==' instead of '='?".

But once we use the equality operator ( == ), the misconception goes away:

Problem solved!

Alright, I think it does it. I hope this quick guide helped you solve your problem.

Thanks for reading.

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SyntaxError: invalid syntax in if statement in Python [Fix]

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Last updated: Apr 8, 2024 Reading time · 4 min

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# SyntaxError: invalid syntax in if statement in Python

The Python "SyntaxError: invalid syntax" is often caused when we use a single equals sign instead of double equals in an if statement.

To solve the error, use double equals == if comparing values and make sure the line of the if statement ends with a colon.

syntaxerror invalid syntax if statement

# Using a single equals sign when comparing

Here is an example of how the error occurs.

using single equals sign

The error is caused because we used a single equals sign instead of double equals.

# Use double equals when comparing values

If comparing values, make sure to use double equals.

use double quotes when comparing values

Always use double equals (==) when comparing values and single equals (=) when assigning a value to a variable.

# Make sure the line of the if statement ends with a colon

Make sure the line of the if statement ends with a colon : .

make sure the line of the if statement ends with colon

If you forget the colon at the end of the line, the error occurs.

# Forgetting to indent your code properly

Another common cause of the error is forgetting to indent your code properly.

Use a tab to indent your code consistently in the entire if block.

properly indent your code

The code in the if statement should be consistently indented.

Never mix tabs and spaces when indenting code in Python because the interpreter often has issues with lines indented using both tabs and spaces.

You can either use tabs when indenting code or spaces, but never mix the two.

# Having an empty block of code

If you need to leave a code block empty before you get to implement it, use a pass statement.

The pass statement does nothing and is used when a statement is required syntactically but the program requires no action.

Using a pass statement is necessary because leaving the else block empty would cause a SyntaxError .

# The code above the if statement might be causing the error

If the error is not resolved, look at the code that's right above the if statement.

Make sure you haven't forgotten to close a parenthesis ) , a square bracket ] or a curly brace } .

The code sample above has a missing closing parenthesis, which causes the error.

Make sure all your quotes "" , parentheses () , curly braces {} and square brackets [] are closed.

# The else statement should also end with a colon

If you have an if/else statement, make sure the else statement also ends with a colon and its code is indented consistently.

If you have an if or else statement that you haven't yet implemented, use a pass statement.

# Make sure you don't have spelling errors

You might get a SyntaxError exception if you have spelling errors.

Python is case-sensitive, so make sure to use lowercase keywords like if and else instead of If or Else .

I've also written an article on how to check for multiple conditions in an if statement .

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

  • Using f-string for conditional formatting in Python
  • Using booleans in an if statement in Python
  • if-elif-else statement on one line in Python
  • Get the first item in a list that matches condition - Python
  • Styling multiline 'if' statements in Python
  • Remove elements from a List based on a condition in Python
  • Check if all/any elements in List meet condition in Python
  • Find the index of Elements that meet a condition in Python
  • Python argparse: unrecognized arguments error [Solved]

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  • Python »
  • 3.12.3 Documentation »
  • The Python Tutorial »
  • 8. Errors and Exceptions
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8. Errors and Exceptions ¶

Until now error messages haven’t been more than mentioned, but if you have tried out the examples you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions .

8.1. Syntax Errors ¶

Syntax errors, also known as parsing errors, are perhaps the most common kind of complaint you get while you are still learning Python:

The parser repeats the offending line and displays little ‘arrow’s pointing at the token in the line where the error was detected. The error may be caused by the absence of a token before the indicated token. In the example, the error is detected at the function print() , since a colon ( ':' ) is missing before it. File name and line number are printed so you know where to look in case the input came from a script.

8.2. Exceptions ¶

Even if a statement or expression is syntactically correct, it may cause an error when an attempt is made to execute it. Errors detected during execution are called exceptions and are not unconditionally fatal: you will soon learn how to handle them in Python programs. Most exceptions are not handled by programs, however, and result in error messages as shown here:

The last line of the error message indicates what happened. Exceptions come in different types, and the type is printed as part of the message: the types in the example are ZeroDivisionError , NameError and TypeError . The string printed as the exception type is the name of the built-in exception that occurred. This is true for all built-in exceptions, but need not be true for user-defined exceptions (although it is a useful convention). Standard exception names are built-in identifiers (not reserved keywords).

The rest of the line provides detail based on the type of exception and what caused it.

The preceding part of the error message shows the context where the exception occurred, in the form of a stack traceback. In general it contains a stack traceback listing source lines; however, it will not display lines read from standard input.

Built-in Exceptions lists the built-in exceptions and their meanings.

8.3. Handling Exceptions ¶

It is possible to write programs that handle selected exceptions. Look at the following example, which asks the user for input until a valid integer has been entered, but allows the user to interrupt the program (using Control - C or whatever the operating system supports); note that a user-generated interruption is signalled by raising the KeyboardInterrupt exception.

The try statement works as follows.

First, the try clause (the statement(s) between the try and except keywords) is executed.

If no exception occurs, the except clause is skipped and execution of the try statement is finished.

If an exception occurs during execution of the try clause, the rest of the clause is skipped. Then, if its type matches the exception named after the except keyword, the except clause is executed, and then execution continues after the try/except block.

If an exception occurs which does not match the exception named in the except clause , it is passed on to outer try statements; if no handler is found, it is an unhandled exception and execution stops with an error message.

A try statement may have more than one except clause , to specify handlers for different exceptions. At most one handler will be executed. Handlers only handle exceptions that occur in the corresponding try clause , not in other handlers of the same try statement. An except clause may name multiple exceptions as a parenthesized tuple, for example:

A class in an except clause matches exceptions which are instances of the class itself or one of its derived classes (but not the other way around — an except clause listing a derived class does not match instances of its base classes). For example, the following code will print B, C, D in that order:

Note that if the except clauses were reversed (with except B first), it would have printed B, B, B — the first matching except clause is triggered.

When an exception occurs, it may have associated values, also known as the exception’s arguments . The presence and types of the arguments depend on the exception type.

The except clause may specify a variable after the exception name. The variable is bound to the exception instance which typically has an args attribute that stores the arguments. For convenience, builtin exception types define __str__() to print all the arguments without explicitly accessing .args .

The exception’s __str__() output is printed as the last part (‘detail’) of the message for unhandled exceptions.

BaseException is the common base class of all exceptions. One of its subclasses, Exception , is the base class of all the non-fatal exceptions. Exceptions which are not subclasses of Exception are not typically handled, because they are used to indicate that the program should terminate. They include SystemExit which is raised by sys.exit() and KeyboardInterrupt which is raised when a user wishes to interrupt the program.

Exception can be used as a wildcard that catches (almost) everything. However, it is good practice to be as specific as possible with the types of exceptions that we intend to handle, and to allow any unexpected exceptions to propagate on.

The most common pattern for handling Exception is to print or log the exception and then re-raise it (allowing a caller to handle the exception as well):

The try … except statement has an optional else clause , which, when present, must follow all except clauses . It is useful for code that must be executed if the try clause does not raise an exception. For example:

The use of the else clause is better than adding additional code to the try clause because it avoids accidentally catching an exception that wasn’t raised by the code being protected by the try … except statement.

Exception handlers do not handle only exceptions that occur immediately in the try clause , but also those that occur inside functions that are called (even indirectly) in the try clause . For example:

8.4. Raising Exceptions ¶

The raise statement allows the programmer to force a specified exception to occur. For example:

The sole argument to raise indicates the exception to be raised. This must be either an exception instance or an exception class (a class that derives from BaseException , such as Exception or one of its subclasses). If an exception class is passed, it will be implicitly instantiated by calling its constructor with no arguments:

If you need to determine whether an exception was raised but don’t intend to handle it, a simpler form of the raise statement allows you to re-raise the exception:

8.5. Exception Chaining ¶

If an unhandled exception occurs inside an except section, it will have the exception being handled attached to it and included in the error message:

To indicate that an exception is a direct consequence of another, the raise statement allows an optional from clause:

This can be useful when you are transforming exceptions. For example:

It also allows disabling automatic exception chaining using the from None idiom:

For more information about chaining mechanics, see Built-in Exceptions .

8.6. User-defined Exceptions ¶

Programs may name their own exceptions by creating a new exception class (see Classes for more about Python classes). Exceptions should typically be derived from the Exception class, either directly or indirectly.

Exception classes can be defined which do anything any other class can do, but are usually kept simple, often only offering a number of attributes that allow information about the error to be extracted by handlers for the exception.

Most exceptions are defined with names that end in “Error”, similar to the naming of the standard exceptions.

Many standard modules define their own exceptions to report errors that may occur in functions they define.

8.7. Defining Clean-up Actions ¶

The try statement has another optional clause which is intended to define clean-up actions that must be executed under all circumstances. For example:

If a finally clause is present, the finally clause will execute as the last task before the try statement completes. The finally clause runs whether or not the try statement produces an exception. The following points discuss more complex cases when an exception occurs:

If an exception occurs during execution of the try clause, the exception may be handled by an except clause. If the exception is not handled by an except clause, the exception is re-raised after the finally clause has been executed.

An exception could occur during execution of an except or else clause. Again, the exception is re-raised after the finally clause has been executed.

If the finally clause executes a break , continue or return statement, exceptions are not re-raised.

If the try statement reaches a break , continue or return statement, the finally clause will execute just prior to the break , continue or return statement’s execution.

If a finally clause includes a return statement, the returned value will be the one from the finally clause’s return statement, not the value from the try clause’s return statement.

For example:

A more complicated example:

As you can see, the finally clause is executed in any event. The TypeError raised by dividing two strings is not handled by the except clause and therefore re-raised after the finally clause has been executed.

In real world applications, the finally clause is useful for releasing external resources (such as files or network connections), regardless of whether the use of the resource was successful.

8.8. Predefined Clean-up Actions ¶

Some objects define standard clean-up actions to be undertaken when the object is no longer needed, regardless of whether or not the operation using the object succeeded or failed. Look at the following example, which tries to open a file and print its contents to the screen.

The problem with this code is that it leaves the file open for an indeterminate amount of time after this part of the code has finished executing. This is not an issue in simple scripts, but can be a problem for larger applications. The with statement allows objects like files to be used in a way that ensures they are always cleaned up promptly and correctly.

After the statement is executed, the file f is always closed, even if a problem was encountered while processing the lines. Objects which, like files, provide predefined clean-up actions will indicate this in their documentation.

8.9. Raising and Handling Multiple Unrelated Exceptions ¶

There are situations where it is necessary to report several exceptions that have occurred. This is often the case in concurrency frameworks, when several tasks may have failed in parallel, but there are also other use cases where it is desirable to continue execution and collect multiple errors rather than raise the first exception.

The builtin ExceptionGroup wraps a list of exception instances so that they can be raised together. It is an exception itself, so it can be caught like any other exception.

By using except* instead of except , we can selectively handle only the exceptions in the group that match a certain type. In the following example, which shows a nested exception group, each except* clause extracts from the group exceptions of a certain type while letting all other exceptions propagate to other clauses and eventually to be reraised.

Note that the exceptions nested in an exception group must be instances, not types. This is because in practice the exceptions would typically be ones that have already been raised and caught by the program, along the following pattern:

8.10. Enriching Exceptions with Notes ¶

When an exception is created in order to be raised, it is usually initialized with information that describes the error that has occurred. There are cases where it is useful to add information after the exception was caught. For this purpose, exceptions have a method add_note(note) that accepts a string and adds it to the exception’s notes list. The standard traceback rendering includes all notes, in the order they were added, after the exception.

For example, when collecting exceptions into an exception group, we may want to add context information for the individual errors. In the following each exception in the group has a note indicating when this error has occurred.

Table of Contents

  • 8.1. Syntax Errors
  • 8.2. Exceptions
  • 8.3. Handling Exceptions
  • 8.4. Raising Exceptions
  • 8.5. Exception Chaining
  • 8.6. User-defined Exceptions
  • 8.7. Defining Clean-up Actions
  • 8.8. Predefined Clean-up Actions
  • 8.9. Raising and Handling Multiple Unrelated Exceptions
  • 8.10. Enriching Exceptions with Notes

Previous topic

7. Input and Output

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Print invalid syntax

Hi, I’m doing a HackerRank exercise, and I keep getting an invalidSyntax with the print command but it won’t explain why it’s invalid:

File “main.py”, line 9 print(i) #testing the print function ^ SyntaxError: invalid syntax

Here is my code. There are parts in hashtag that are my previous attempts that I’ve left there in case they can be used again, but don’t mind it. Because this is a HackerRank exercise, the part of the code that I labeled at the end cannot be edited, but I don’t think this has to do with the invalid syntax…

What happens when you remove the code that gave you the syntax error?

When I removed both the print lines below “printer” I got: File “main.py”, line 11 def deci(a): ^ SyntaxError: invalid syntax

P.S. I didn’t think of checking how it would go if the print commands weren’t there. Thank you.

Also after removing the 4 def lines, I got:

File “main.py”, line 22 if name == ‘ main ’: ^ SyntaxError: invalid syntax

Shouldn’t the permanent section of the exercise be totally correct?

Keep going, remove that, too.

After removing the 4 def lines, I got:

What’s the point of saying that again?

I’m sorry, the point of saying what? If you mean the fact that I replied twice it was an error, I’m sorry, I thought the first time it didn’t post.

Yes, I meant the duplicate post.

Oh, I’m very sorry then. A lot of times when I use iMessage the text looks like it’s posted but then takes a while to notify me and show the not sended red message. I don’t have much experience using other post platforms so… again, sorry.

As amusing (and educational) as it may be to do this line by line, I’ll give you a hint:

:joy:

I think they were almost there. I just don’t know why it’s taking them over 20 minutes to remove the last few lines, too.

General tip: If you get a syntax error and the line it’s pointing to doesn’t look wrong, move up a little. The error is often a simple one on the previous line (a forgotten close bracket of some form, a dangling operator, etc). This is true in all languages; you’ll find the same thing in JavaScript or C, too.

The easiest way to figure out if that’s the problem is what @Stefan2 initially suggested: Remove the line of code that is reporting the error. If the error instantly moves down to the next line, there’s a VERY high chance that the bug is actually a line above it.

Almost all programmers’ editors have some sort of tool for helping you match parentheses (colouring them differently, or showing the one that pairs with the one next to the cursor, or something). Get to know how your editor shows this. If the editor disagrees with your expectations about the code, that’s a really good sign that there’s a bug!

Yes, that was the goal/plan. Had they kept going and removed all the rest, they finally would’ve realized there must be a problem in the code above . I think that’s still a valuable exercise to do once, even if in the future your “If the error instantly moves down [then look above ]” rule is what you do.

Stefan2, abessman, and Rosuav , thank you all for your advice! It’s been really helpful.

Yup! I figured that was your intent, but in case the OP hadn’t picked up on that, I wanted to elaborate.

:slight_smile:

Oh that reminds me. In Python 3.12, I actually got this for their full original code:

@Rosuav , I love that reference! And thank you for your encouragement. I know this isn’t really related to Python, but I just wanted to say I really appreciated it. Your comments give off a very positive vibe.

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  1. eval SyntaxError: invalid syntax in python

    26. eval() only allows for expressions. Assignment is not an expression but a statement; you'd have to use exec instead. Even then you could use the globals() dictionary to add names to the global namespace and you'd not need to use any arbitrary expression execution. You really don't want to do this, you need to keep data out of your variable ...

  2. PEP 572

    Unparenthesized assignment expressions are prohibited for the value of a keyword argument in a call. Example: foo(x = y := f(x)) # INVALID foo(x=(y := f(x))) # Valid, though probably confusing. This rule is included to disallow excessively confusing code, and because parsing keyword arguments is complex enough already.

  3. Invalid Syntax in Python: Common Reasons for SyntaxError

    Note: The examples above are missing the repeated code line and caret (^) pointing to the problem in the traceback.The exception and traceback you see will be different when you're in the REPL vs trying to execute this code from a file. If this code were in a file, then you'd get the repeated code line and caret pointing to the problem, as you saw in other cases throughout this tutorial.

  4. The Walrus Operator: Python 3.8 Assignment Expressions

    Each new version of Python adds new features to the language. For Python 3.8, the biggest change is the addition of assignment expressions.Specifically, the := operator gives you a new syntax for assigning variables in the middle of expressions. This operator is colloquially known as the walrus operator.. This tutorial is an in-depth introduction to the walrus operator.

  5. How To Use Assignment Expressions in Python

    The author selected the COVID-19 Relief Fund to receive a donation as part of the Write for DOnations program.. Introduction. Python 3.8, released in October 2019, adds assignment expressions to Python via the := syntax. The assignment expression syntax is also sometimes called "the walrus operator" because := vaguely resembles a walrus with tusks. ...

  6. How do Assignment Expressions `:=` work in Python?

    13. I've read PEP 572 about assignment expressions and I found this code to be a clear example where I could use it: while line := fp.readline(): do_stuff(line) But I am confused, from what I read, it is supposed to work just like normal assignment but return the value. But it doesn't appear to work like that: >>> w:=1.

  7. Python's Assignment Operator: Write Robust Assignments

    To create a new variable or to update the value of an existing one in Python, you'll use an assignment statement. This statement has the following three components: A left operand, which must be a variable. The assignment operator ( =) A right operand, which can be a concrete value, an object, or an expression.

  8. Python 101

    Assignment expressions were added to Python in version 3.8. The general idea is that an assignment expression allows you to assign to variables within an expression. The syntax for doing this is: NAME := expr. This operator has been called the "walrus operator", although their real name is "assignment expression".

  9. SyntaxError: cannot assign to expression here. Maybe you meant

    # SyntaxError: cannot assign to literal here (Python) The Python "SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?" occurs when we try to assign to a literal (e.g. a string or a number). To solve the error, specify the variable name on the left and the value on the right-hand side of the assignment.

  10. Support Assignment Expression ("walrus" operator) syntax #8530

    Assignment Expressions are a new feature added with Python 3.8. Currently, the VS Code Python Extension auto-corrects this syntax into invalid syntax, i.e. the colon is shifted left to be positioned on the right-most end of the assignee in the expression (to fit with "normal" colon usage in Python), putting a space between itself and the equal sign, forcing the user to Ctrl-Z the change each time.

  11. 7. Simple statements

    Simple statements — Python 3.12.3 documentation. 7. Simple statements ¶. A simple statement is comprised within a single logical line. Several simple statements may occur on a single line separated by semicolons. The syntax for simple statements is: simple_stmt ::= expression_stmt. | assert_stmt.

  12. What's New In Python 3.8

    Editor, Raymond Hettinger,. This article explains the new features in Python 3.8, compared to 3.7. Python 3.8 was released on October 14, 2019. ... Assignment expressions¶ There is new syntax : ... , compile() will allow top-level await, async for and async with constructs that are usually considered invalid syntax. Asynchronous code object ...

  13. PEP 379

    The translation of the proposed syntax is: VAR = (EXPR) (EXPR) The assignment target can be either an attribute, a subscript or name: f() -> name[0] # where 'name' exists previously. f() -> name.attr # again 'name' exists prior to this expression. f() -> name. This expression should be available anywhere that an expression is currently accepted ...

  14. Python eval(): Evaluate Expressions Dynamically

    Python's eval() allows you to evaluate arbitrary Python expressions from a string-based or compiled-code-based input. This function can be handy when you're trying to dynamically evaluate Python expressions from any input that comes as a string or a compiled code object.. Although Python's eval() is an incredibly useful tool, the function has some important security implications that you ...

  15. [Solved] SyntaxError: cannot assign to expression here in Python

    Using an invalid name (identifier) in an assignment statement: Assignment statements bind names to values. (e.g., total_price = 49.99) Based on Python syntax and semantics, the left-hand side of the assignment operator (=) should always be an identifier, not an expression or a literal.

  16. About Dictionary Based Syntax Errors~Python 3.10

    I was working on a new project which was based on dictionaries and recognized some weird(?) things about syntax errors which pop out when you do not separate the key:value pairs with commas. I have created an example to ask my question better: # Dummy Keys key = "Jules" key2 = "Potato" key3 = "Doctor" key4 = "Computer" key5 = "Chair" key6 = "Answers" no_comma_dict1 = { key: { key2: "Please put ...

  17. SyntaxError: invalid syntax in if statement in Python [Fix]

    # SyntaxError: invalid syntax in if statement in Python. The Python "SyntaxError: invalid syntax" is often caused when we use a single equals sign instead of double equals in an if statement. To solve the error, use double equals == if comparing values and make sure the line of the if statement ends with a colon. # Using a single equals sign ...

  18. 8. Errors and Exceptions

    The exception's __str__() output is printed as the last part ('detail') of the message for unhandled exceptions.. BaseException is the common base class of all exceptions. One of its subclasses, Exception, is the base class of all the non-fatal exceptions.Exceptions which are not subclasses of Exception are not typically handled, because they are used to indicate that the program should ...

  19. python 3.x

    assignment_stmt ::= (target_list "=")+ (starred_expression | yield_expression) augmented_assignment_stmt ::= augtarget augop ( expression_list | yield_expression) So here is a difference in the specifications of an assignment and an augmented assignment - the latter has expression_list instead of starred_expression .

  20. Assignment Expression Syntax

    Assignment Expression Syntax. For more information on concepts covered in this lesson, you can check out: Walrus operator syntax. One of the main reasons assignments were not expressions in Python from the beginning is the visual likeness of the assignment operator (=) and the equality comparison operator (==). This could potentially lead to bugs.

  21. Print invalid syntax

    Hi, I'm doing a HackerRank exercise, and I keep getting an invalidSyntax with the print command but it won't explain why it's invalid: File "main.py", line 9 print(i) #testing the print function ^ SyntaxError: invalid syntax Here is my code. There are parts in hashtag that are my previous attempts that I've left there in case they can be used again, but don't mind it. Because ...

  22. What exactly is "invalid syntax" and why do I keep getting it in Python

    9 1 1 1. Invalid syntax simply means that the code you have written cannot be interpreted as valid instructions for python. "Syntax" refers to the rules and structures of a language, normally spoken, but also in programming. - ApproachingDarknessFish.