导入错误：无法从“键入”导入名称“文字”

Question

I have recently started using PEP 484 and PEP 586 to make my code clearer and more accessible. So far everything was ok, but when I wanted to use Literal from the package typing it appears it couldn't be imported. What is the most surprising is that PyCharm isn't complaining at all for importing it or using it.

The code I want to use in the end is looking like that:

SomeVar = TypeVar("SomeVar", Literal['choice1'], Literal['choice2'], someType)

It would be used in the cases where you can have a string to describe what you want or an already made solution eg:

def someFunc(my_var: SomeVar = 'choice1'):
    result = []
    if my_var == 'choice1':
        result.append(...)
    else:
        result = my_var
    return result

I use an Anaconda environment with Python 3.7.7.

Answer 1

Using Literal in Python 3.8 and later

from typing import Literal

Using Literal in all Python versions (1)

Literal was added to typing.py in 3.8, but you can use Literal in older versions anyway.

First install typing_extensions ( pip install typing_extensions ) and then

from typing_extensions import Literal

This approach is supposed to work also in Python 3.8 and later.

Using Literal in all Python versions (2)

For completeness, I'm also adding the try-except approach to import Literal :

try:
    from typing import Literal
except ImportError:
    from typing_extensions import Literal

This should also work for all Python versions, given that typing_extensions is installed if you're using Python 3.7 or older.

Answer 2

As stated in the docs , typing.Literal is only available from Python 3.8 and up.