Using modern typing features on older versions of Python

Question

So, I was writing an event emitter class using Python.

Code currently looks like this:

from typing import Callable, Generic, ParamSpec

P = ParamSpec('P')

class Event(Generic[P]):
  def __init__(self):
    ...

  def addHandler(self, action : Callable[P, None]):
    ...

  def removeHandler(self, action : Callable[P, None]): 
    ...

  def fire(self, *args : P.args, **kwargs : P.kwargs):
    ...

As you can see, annotations depend on ParamSpec, which was added to typing in python 3.10 only.

And while it works good in Python 3.10 (on my machine), it fails in Python 3.9 and older (on other machines) because ParamSpec is a new feature.

So, how could I avoid importing ParamSpec when running program or use some fallback alternative, while not confusing typing in editor (pyright)?

Answer 1

I don't know if there was any reason to reinvent the wheel, but typing_extensions module is maintained by python core team, supports python3.7 and later and is used exactly for this purpose. You can just check python version and choose proper import source:

import sys

if sys.version_info < (3, 10):
    from typing_extensions import ParamSpec
else:
    from typing import ParamSpec