eval_type_backport

This package makes runtime typing inspection with the typing module possible with newer syntax in older Python versions. Specifically, this transforms X | Y into typing.Union[X, Y] and list[X] into typing.List[X] etc. (for all the types made generic in PEP 585) if the original syntax is not supported in the current Python version.

For users of Pydantic, merely having this package installed should make Pydantic models with newer syntax work in older Python versions.

Here's an example of how to use it directly:

import typing

from eval_type_backport import install_patch

install_patch()


class Foo:
    a: 'int | str'


print(typing.get_type_hints(Foo))

In Python 3.9, without the install_patch, the above code will raise TypeError: unsupported operand type(s) for |: 'type' and 'type'. With it, it prints {'a': typing.Union[int, str]} as expected.

install_patch monkey-patches the typing module so that things should 'just work' from wherever. To specifically use the backport where you need it instead of patching globally, you can use the eval_type_backport.eval_type_backport function directly instead of typing._eval_type. Yes, typing._eval_type is a protected function that you shouldn't normally be using. This package was written to support Pydantic, which uses it internally.

Install

From PyPI:

pip install eval-type-backport

or with Conda:

conda install -c conda-forge eval-type-backport