Work related to PEP 484: (released via PyPI) and issue tracker
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erikwright and ilevkivskyi Fix instance/subclass checks of functions against runtime protocols. (#…

Fixes #579 .

When performing an `issubclass` check of a type against a protocol, the `__annotations__` member of the type is accessed and assumed to be iterable. `__annotations__` is a descriptor in the case of `types.FunctionType`, so while it is iterable when accessed on a function instance it is not iterable when accessed on the type of a function. This causes the `issubclass` check to fail with an exception.

In some cases (AFAICT, non-data protocols), an `isinstance` check of an object will use, internally, a subclass check of the object's type. As a result, `isinstance` will also fail with an exception in these conditions.

The above only seemed to occur in Python 3.

This PR fixes the issue in the Python 3 implementation while adding test coverage for both Python 2 and 3 that ensures that functions (and `types.FunctionType`) can be correctly compared both against protocols that they legitimately implement as well as those that they do not implement.
Latest commit 9443f26 Oct 11, 2018


PEP 484: Type Hints

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This GitHub repo is used for development of the typing module defined by PEP 484. The module is available in Python since version 3.5.0 on a provisional basis until Python 3.7.0.


  • Guido van Rossum
  • Jukka Lehtosalo
  • Łukasz Langa


The BDFL-Delegate is Mark Shannon. He was the final reviewer of PEP 484 and ultimately accepted it on May 22, 2014.

Important dates

  • May 24, 2015: Python 3.5.0 beta 1 -- PEP 484 accepted, typing checked into the CPython repo
  • September 13, 2015: Python 3.5.0 final release; typing is available on a provisional basis
  • December 23, 2016: Python 3.6.0 final release; typing stays provisional for the course of the 3.6 releases
  • January 29, 2018: Python 3.7.0 beta 1, feature freeze for the release, including the typing module
  • June 15, 2018: Python 3.7.0 final release, the typing module is no longer provisional

The dates for Python 3.7 are based on PEP 537 and may still change.

Important URLs

The rendering of PEP 484 lives at

Two related informational PEPs exist:

The site automatically updates (with a slight delay, typically in the order of 5-60 minutes) whenever the python/peps repo is updated.


  • The module and its unittests are edited in the src subdirectory of this repo. The python2 subdirectory contains the Python 2 backport.
  • The PEPs 484, 483, and 482 are edited in the GitHub python/peps repo.
  • Use the GitHub issue tracker for this repo to collect concerns and TO DO items for PEPs 484, 483, and 482 as well as for
  • Accumulate changes in the GitHub repo, closing issues as they are either decided and described in PEP 484, or implemented in, or both, as befits the issue. (Some issues will be closed as "won't fix" after a decision is reached not to take action.)
  • Make frequent small commits with clear descriptions. Preferably use a separate commit for each functional change, so the edit history is clear, merge conflicts are unlikely, and it's easy to roll back a change when further discussion reverts an earlier tentative decision that was already written up and/or implemented.
  • Push to GitHub frequently.
  • Pull from GitHub frequently, rebasing conflicts carefully (or merging, if a conflicting change was already pushed).
  • At reasonable checkpoints: post current versions of PEPs to python-dev, making sure to update the Post-History header in python/peps repo. This is typically done by Guido.

Tracker labels

  • bug: Needs to be fixed in
  • to do: Editing task for PEP 484 or for this repo.
  • enhancement: Proposed new feature.
  • postponed: Idea up for discussion.
  • out of scope: Somebody else's problem.

Workflow for mypy changes

  • Use the GitHub issue tracker for the mypy repo (python/mypy). The mypy core developers accept pull requests at their discretion.
  • mypy uses from the available standard library when ran on Python 3.5+ and uses the PyPI version for older Python versions
  • The full list of mypy issues marked as PEP 484 compatibility issues is here:

Workflow for CPython changes

  • At Guido's discretion, he will from time to time copy and from the python/typing GitHub repo to the cpython repo.
  • This process includes merging changes made directly in the cpython repo by other core developers.
  • The changes are merged in three branches (3.5, 3.6, default) due to the module's provisional status.

Workflow for PyPI releases

  • Run tests under all supported versions. As of March 2017 this includes 2.7, 3.3, 3.4, 3.5, 3.6.
  • On macOS, you can use pyenv to manage multiple Python installations. Long story short:
    • xcode-select --install
    • brew install pyenv
    • echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
    • Open a new shell
    • pyenv install 3.5.3
    • pyenv install 3.4.6
    • pyenv install 3.3.6
    • (assuming you already have 2.7.13 and 3.6.1 from Homebrew)
    • pyenv global system 3.5.3 3.4.6 3.3.6
  • You can use tox to automate running tests.
  • Update the version number in
  • Build the source and wheel distributions:
    • pip3 install -U setuptools wheel
    • pip2 install -U setuptools wheel
    • rm -rf dist/ build/
    • python3 sdist bdist_wheel
    • rm -rf build/ (Works around a Wheel bug)
    • python2 bdist_wheel
  • Install the built distributions locally and test (if you were using tox, you already tested the source distribution).
  • Make sure twine is up to date, then run twine upload dist/*.