For a new Python project using the latest version of Python should I declare my types as upper or lower case


According to pep-0585 for the latest versions of Python, it appears we can use List and list interchangeably for type declarations. So which should I use?


  1. no requirement for backward compatibility
  2. using the latest version of python
from typing import List

def hello_world_1(animals: list[str]) -> list[str]:
    return animals

def hello_world_2(animals: List[str]) -> List[str]:
    return animals

How can I set up a python linter to enforce consistency and only allow either upper or lowercase List for example?

Asked By: MattG



In general … it is your choice. AFAIK, there is no PEP recommendation on which one to use.

If you have decided to use generic type hinting:

  • Prior to python 3.9 you had to use typing.List (for example)
  • From python 3.9 onward you can use either list or typing.List. Again … your choice.

(If you are asking for our recommendations, that is explicitly off-topic for StackOverflow! Maybe discuss it with your co-workers, other people working on your projects, …)

Answered By: Stephen C

PEP585 (linked in the OP) described the imports from typing as cumbersome and confusing. This seems to answer the question of which style is preferred.

Answered By: benjimin

According to the current Python docs, typing.List and similar are deprecated.

The docs further state

The deprecated types will be removed from the typing module in the first Python version released 5 years after the release of Python 3.9.0. See details in PEP 585—Type Hinting Generics In Standard Collections.

Concerning enforcing consistency, it says

It is expected that type checkers will flag the deprecated types when the checked program targets Python 3.9 or newer.

However, I use Pylint personally (not a type checker, admittedly) and I don’t believe I’ve noticed it flagging the deprecated types yet.

Answered By: msailor
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