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Type annotations for the Traits package

Project description

The traits-stubs package contains external type annotations for the Traits package. These annotations can be used with static type checkers like mypy to type-check your Traits-using Python code.


  • To install from PyPI, simply use pip install traits-stubs.

  • To install from source, run pip install . from this directory.


You’ll usually want to install mypy (or another type checker) into your Python environment alongside these stubs. You can then use mypy from the command line to check a file or directory, for example with:

mypy <>

Alternatively, some IDEs (including VS Code and PyCharm) can be configured to perform type checking as you edit.


To test traits stubs locally:

  • Create a fresh venv and activate it, for example with:

    $ python -m venv --clear ~/.venvs/traits-stubs && source ~/.venvs/traits-stubs/bin/activate
  • Make sure all build-related packages are up to date

    $ python -m pip install –upgrade pip setuptools wheel

  • Install the Traits library into the environment (non-editable install)

    $ python -m pip install .

  • Install traits stubs in editable mode (from the repo, not from PyPI).

    $ python -m pip install -e traits-stubs/

  • Install mypy (or your favourite type checker)

    $ python -m pip install mypy

  • From the traits-stubs directory, run mypy on individual files in traits_stubs_tests/examples with e.g.,

    $ python -m mypy traits_stubs_tests/examples/

  • From the traits-stubs directory, run the test suite with:

    $ python -m unittest discover -v traits_stubs_tests

Note: it’s easy to get confusing results if you accidentally use the wrong version of mypy. To avoid that, you can make sure that you don’t have mypy installed globally, and/or always invoke mypy using python -m mypy from within the environment.

Note: the unittest run can give the wrong result in the presence of a stale .mypy_cache. If you’re getting a pass where you expect to get a failure (or vice versa), try deleting the local cache and trying again.


This package depends on Traits.

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