PEP585 Upgrade

This is a pre-commit hook configured to automatically upgrade your type hints to the new native types implemented in PEP 585.

This will work for Python 3.8 and above, though if you're using 3.8 specifically you will need to run the hook with futures-imports=true.

A complete type list is shown below.

See the complete list

I'm a visual learner

In a nutshell, this code

from typing import List, Tuple, Dict, Set, FrozenSet

def do_thing(x: List[Tuple[str, ...]], y: Dict[str, Set[str]]) -> FrozenSet:

becomes this

def do_thing(x: list[tuple[str, ...]], y: dict[str, set[str]]) -> frozenset:

or this, if you're running python < 3.9 or enable the futures option

from __future__ import annotations

def do_thing(x: list[tuple[str, ...]], y: dict[str, set[str]]) -> frozenset:


  • Performs in-line substitution for new types
  • Adds new imports for upgrade types which need them
  • Adds __futures__ imports if the futures flag is enabled
  • Removes no longer needed typing imports

Note: even though we remove and add imports reasonably well, I would recommend running this in tandem with hooks like isort to aggregate and sort your imports, and flake8 to discover any unused imports neither were able to remove. Otherwise you risk needing to do some manual cleanup from time to time (though it should be pretty rare).


To use this with pre-commit, simply add this to your config file:

- repo:
  rev: ''  # Use the sha / tag you want to point at
  - id: upgrade-type-hints

and while futures imports are added automatically if you're running Python older than 3.9, you can also enable them explicitly, by adding a --futures arg.

This is required, e.g., when maintaining code that needs to support older Python versions.

- repo:
  rev: ''  # Use the sha / tag you want to point at
  - id: upgrade-type-hints
    args: [ '--futures=true' ]

For more information about available arguments, see the function definitions.

Running this once on my codebase

If you wish to run this once on your codebase, that's not easy to do without pre-commit, as it piggybacks on that process quite a bit.

However, installing pre-commit and configuring the hook to run will take you less than a minute. These are the steps:

  • Run pip install pre-commit
  • Run touch .pre-commit-config.yaml
  • Copy the configuration shown above into the file
  • Run pre-commit run --all-files

Running this once on a single file

To run the upgrade on a single file, you can clone the repo and run python -m upgrade_type_hints <filename> from the src folder, or something equivalent.

Known imperfections

  • We have a hard time removing common import typing imports, since we don't have a full inventory of all possible places typing could be used. Seeing something like this, you might think this is easy to handle

    import typing
    x: typing.List

    but extending this example to a thousand-line file, the way we've structured the logic, there is no way to know whether there is a valid typing.Optional somewhere in the file.

  • We might remove typing imports in a file where you needed them for more than just type annotations. An example of this is custom type declarations:

    from typing import List
    x: List  # this will be upgraded and the import will be removed
    y = List[str]  # this will be left without its required import

    The reason for this is that custom type declarations are not a part of the ast objects we look at.

Both points are resolved by running flake8.