Generator expression must be parenthesized питон

SyntaxError: Generator expression must be parenthezised / python manage.py migrate

I’m really new in programming and I wanted to follow the Djangogirls tutorial, but I’m stucked now. In the tutorial, I am here:

To create a database for our blog, let’s run the following in the console: python manage.py migrate (we need to be in the djangogirls directory that contains the manage.py file). If that goes well, you should see something like this: .

(myvenv) C:\Users\Julcsi\djangogirls> python manage.py migrate Traceback (most recent call last): File "manage.py", line 22, in execute_from_command_line(sys.argv) File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\core\management\__init__.py", line 364, in execute_from_command_line utility.execute() File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\core\management\__init__.py", line 338, in execute django.setup() File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\__init__.py", line 27, in setup apps.populate(settings.INSTALLED_APPS) File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\apps\registry.py", line 85, in populate app_config = AppConfig.create(entry) File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\apps\config.py", line 94, in create module = import_module(entry) File "C:\Users\Julcsi\AppData\Local\Programs\Python\Python37\lib\importlib\__init__.py", line 127, in import_module return _bootstrap._gcd_import(name[level:], package, level) File "", line 994, in _gcd_import File "", line 971, in _find_and_load File "", line 955, in _find_and_load_unlocked File "", line 665, in _load_unlocked File "", line 723, in exec_module File "", line 219, in _call_with_frames_remove File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\contrib\admin\__init__.py", line 4, in from django.contrib.admin.filters import ( File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\contrib\admin\filters.py", line 10, in from django.contrib.admin.options import IncorrectLookupParameters File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\contrib\admin\options.py", line 12, in from django.contrib.admin import helpers, widgets File "C:\Users\Julcsi\djangogirls\myvenv\lib\site-packages\django\contrib\admin\widgets.py", line 152 '%s=%s' % (k, v) for k, v in params.items(), SyntaxError: Generator expression must be parenthesized 

What am I doing wrong? What should I do? I have Python 3.7.0b1 Thanks a lot in advance for the help 🙂

Источник

Generator expression must be parenthesized питон

Last updated: Jun 9, 2023
Reading time · 3 min

# Table of Contents

# Generator expressions must be parenthesized if not sole argument

The Python error «Generator expressions must be parenthesized if not sole argument» occurs when you pass a non-parenthesized generator expression as an argument to a function that takes multiple arguments.

To solve the error, wrap the generator expression in parentheses and make sure you haven’t misplaced your parentheses.

Here is an example of how the error occurs.

Copied! 
def example(gen, num): print(gen) print(num) # ⛔️ Generator expressions must be parenthesized if not sole argument # ⛔️ SyntaxError: Generator expression must be parenthesized example(num for num in range(3), 10) 

The function takes 2 arguments — a generator expression and a number.

We called the function with the two required arguments but we didn’t wrap the generator expression in parentheses which caused the error.

Generator expressions must be wrapped in parentheses if they are not the sole function argument.

Copied! 
def example(gen, num): print(gen) print(num) example((num for num in range(3)), 10) 

We wrapped the generator expression argument in parentheses which resolved the issue.

Wrapping the generator expression in parentheses has a couple of advantages:

1. It makes your code easier to read.
2. It makes your code easier for Python to parse.
3. Python is able to compute the generator expression argument.

If you meant to pass a list to the function, you can wrap the generator expression in square brackets [] to use a list comprehension instead.

Copied! 
def example(gen, num): print(gen) print(num) example([num for num in range(3)], 10) 

Wrapping the generator expression in square brackets [] makes it a list comprehension.

List comprehensions are used to perform some operation for every element, or select a subset of elements that meet a condition.

If the function takes a single argument, then you don’t have to parenthesize the generator expression.

Copied! 
def example(gen): print(gen) example(num for num in range(3)) 

# Make sure you don’t have a trailing comma after the generator expression

The error is also caused if you mistakenly place a trailing comma after the generator expression, in the function call.

Copied! 
def example(gen): print(gen) # ⛔️ Generator expressions must be parenthesized if not sole argument # ⛔️ SyntaxError: Generator expression must be parenthesized example(num for num in range(3), ) # 👈️ trailing comma 

Notice that there is a trailing comma after the generator expression in the call to the example() function.

1. If the function takes 2 parameters one of which is a generator expression, then you have to wrap the generator expression in parentheses and supply the second argument.

Copied! 
# ✅ Works as expected def example(gen, num): print(gen) # at 0x7f27e6b44580> print(num) # 10 example((num for num in range(3)), 10) 

1. If the function only takes a single parameter which is a generator expression, then remove the trailing comma.

Copied! 
# ✅ Works as expected def example(gen): print(gen) # at 0x7f27e6b44580> example(num for num in range(3)) 

# Make sure you haven’t misplaced the parentheses when calling a function

Another common cause of the error is misplacing the parentheses when calling a function.

Copied! 
def example(a, b): return a * b # ⛔️ Generator expressions must be parenthesized if not sole argument # ⛔️ SyntaxError: Generator expression must be parenthesized a_list = [example(num, num + 1 for num in range(3))] 

The code sample causes the error because we are trying to call the example() function with a number and a generator expression that is not parenthesized.

Instead, I meant to call the function for each number in range(3) .

Copied! 
# ✅ Works as expected def example(a, b): return a * b a_list = [example(num, num + 1) for num in range(3)] print(a_list) # 👉️ [0, 2, 6] 

I placed the closing parenthesis ) after the num + 1 expression.

This solves the error because we call the function with two numbers for each iteration of the range() sequence.

# Additional Resources

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

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

Источник

Syntaxerror generator expression must be parenthesized

The syntaxerror generator expression must be parenthesized typically happens when working with generator expressions in Python.

This error message is easy to fix. However, it’s a little bit confusing, especially if you are new to this.

Fortunately, this article discusses how to fix the generator expression must be parenthesized error message.

What is generator expressions?

Generator expression is a concise method for creating a generator object. It resembles a list comprehension, but instead of generating a complete list, it generates a generator object. This generator object can be iterated over to produce values as needed.

Generator expressions are typically written within parentheses, and they allow you to iterate over a sequence, apply transformations or filters, and produce a series of values without storing them all in memory at once.

For example:

generator = (num ** 3 for num in range(10)) for num in generator: print(num)

0 1 8 27 64 125 216 343 512 729

What is “syntaxerror generator expression must be parenthesized”?

The syntaxerror: generator expression must be parenthesized is an error message that occurs in Python when a generator expression is used as an argument in a function call but it is not the only argument and it is not enclosed in parentheses.

For example:

r = ooPoint((v, x[S.oovar_indexes[i]:S.oovar_indexes[i+1]]) for i, v in enumerate(S._variables), **kw) 

 File "C:\Users\pies-pc2\PycharmProjects\pythonProject\main.py", line 1 r = ooPoint((v, x[S.oovar_indexes[i]:S.oovar_indexes[i+1]]) for i, v in enumerate(S._variables), **kw) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ SyntaxError: Generator expression must be parenthesized 

Why does the “generator expression must be parenthesized” syntaxerror occur?

The syntaxerror: generator expression must be parenthesized error occurs when you used the generator expression as an argument in a function call, however it is not the only argument and it is not enclosed in parentheses.

It is because the Python interpreter needs to be able to distinguish between the generator expression and the other arguments in the function call.

By adding parentheses around the generator expression, you make it clear to the interpreter that the generator expression is a single argument.

How to fix the “syntaxerror generator expression must be parenthesized”?

Here are following solutions to fix the generator expression must be parenthesized error message with sample code and results along with a simple explanation:

Solution 1: Add parentheses around the generator expression

This is the most straightforward solution. Simply add parentheses around the generator expression to make it clear to the Python interpreter that it is a single argument in the function call.

Incorrect code:

generator = (num ** 3 for num in range(10)) for num in generator: print(num)

Corrected code:

r = ooPoint(((v, x[S.oovar_indexes[i]:S.oovar_indexes[i+1]]) for i, v in enumerate(S._variables)), **kw)

Solution 2: Assign the generator expression to a variable

You can assign the generator expression to a variable and then pass that variable as an argument to the function call.

Incorrect code:

sum(x ** 3 for x in range(20))

Corrected code:

sample= (a ** 3 for a in range(20)) sum(gen)

You can also use the following code:

gen_expr = (x ** 3 for x in range(5)) squares = list(gen_expr) print(squares) 

[0, 1, 8, 27, 64]

Solution 3: Use a list comprehension instead of a generator expression

You can use a list comprehension instead of a generator expression. List comprehensions do not need to be enclosed in parentheses when used as arguments in function calls.

Incorrect code:

sum(x ** 2 for x in range(10))

Corrected code:

sum([x ** 3 for x in range(20)])

Solution 4: Use the built-in map function instead of a generator expression

You can also use the built-in map function to apply a function to each element in an iterable and then pass the result to the sum function.

Incorrect code:

sum(x ** 2 for x in range(10))

Corrected code:

sum(map(lambda x: x ** 2, range(10)))

Conclusion

In conclusion, the syntaxerror: generator expression must be parenthesized is an error message that occurs in Python when a generator expression is used as an argument in a function call but it is not the only argument and it is not enclosed in parentheses.

This article already provides solutions to fix this error message. By executing the solutions above, you can master this SyntaxError with the help of this guide.

We are hoping that this article helps you fix the error. Thank you for reading itsourcecoders 😊

Leave a Comment Cancel reply

You must be logged in to post a comment.

Источник