python / python/typing

Wrapper/Proxy Generic Type

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topic: feature
Dominant language
Python
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Description

I've been putting some work into typeshed pull requests and I've noticed some places where I could really have used a Proxy Generic class - meaning I can inherit from Proxy[T] and that means that whatever attributes T has, Proxy[T] also has. We don't want to directly mark this as inheritance since then the distinction of a proxy is lost.

The examples I ran into are ProxyType and CallableProxyType in weakref or SynchronizedBase in multiprocessing,csharedtypes.
A big one would be unittest.Mock (See https://github.com/python/mypy/issues/1188).
I'm sure other cases exist,

Advantages:

  • Representing a proxy type easily
  • Allowing type checkers to enforce typing

Disadvantages:

  • Functions that get T won't accept Proxy[T] as an argument. Although the current state is probably something similar.

I'd really like to hear some opinions on the idea.

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Research direction

Start by reading the proposal and its discussion, including the examples involving weakref, multiprocessing.sharedctypes, and unittest.Mock, plus the linked mypy issue. A useful outcome would require agreement on whether Proxy[T] belongs in the typing design and a clear specification of its behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
tooling
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Quiet
Clarity
Needs clarification
Newbie friendliness
25/100

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