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In adding type hints to python functions which is preferred?

from typing import List, Dict

def example_1() -> List[Dict]:
    pass

def example_2() -> List[dict]:
    pass

I know that if I wanted to specify the key and value types in the dict I'd need to use Dict, but I don't want to.

Is there any difference between the two? If so, which is preferred?

Keverly
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  • Oh, I didn't know that. Which version was that introduced in? – Keverly Jun 30 '21 at 17:30
  • I'm voting to mark this as duplicate of [Difference between defining typing.Dict and dict?](https://stackoverflow.com/questions/37087457/difference-between-defining-typing-dict-and-dict) – mkrieger1 Jan 13 '23 at 02:17

2 Answers2

30

Since Python 3.9, the standard collections can be subscripted. The typing variants are now deprecated as a result:

tuple # typing.Tuple

list # typing.List

dict # typing.Dict

set # typing.Set

...

Importing those from typing is deprecated. Due to PEP 563 and the intention to minimize the runtime impact of typing, this deprecation will not generate DeprecationWarnings. Instead, type checkers may warn about such deprecated usage when the target version of the checked program is signalled to be Python 3.9 or newer. It's recommended to allow for those warnings to be silenced on a project-wide basis.

The deprecated functionality will be removed from the typing module in the first Python version released 5 years after the release of Python 3.9.0.

Carcigenicate
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6

There is no practical difference in terms of how it affects type coverage.

As a matter of style/readability, I would suggest using Dict[Any, Any] (or dict[Any, Any] if you're on a version that supports that), since it makes it more obvious to the reader that there is no type checking on the keys and values of the dict. Novices may not understand how unsafe a bare dict/Dict type is but are more likely to recognize the danger if they see the Any in there.

Samwise
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