Hello, V2 of my PEP on packaging type information is available at https://www.python.org/dev/peps/pep-0561/. It is also replicated below. I look forward to any suggestions or comments that people may have! Thanks Ethan ----------------------------------------------------------------------- PEP: 561 Title: Distributing and Packaging Type Information Author: Ethan Smith <ethan@ethanhs.me> Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 09-Sep-2017 Python-Version: 3.7 Post-History: Abstract ======== PEP 484 introduced type hints to Python, with goals of making typing gradual and easy to adopt. Currently, typing information must be distributed manually. This PEP provides a standardized means to package and distribute type information and an ordering for type checkers to resolve modules and collect this information for type checking using existing packaging architecture. Rationale ========= Currently, package authors wish to distribute code that has inline type information. However, there is no standard method to distribute packages with inline type annotations or syntax that can simultaneously be used at runtime and in type checking. Additionally, if one wished to ship typing information privately the only method would be via setting ``MYPYPATH`` or the equivalent to manually point to stubs. If the package can be released publicly, it can be added to typeshed [1]_. However, this does not scale and becomes a burden on the maintainers of typeshed. Additionally, it ties bugfixes to releases of the tool using typeshed. PEP 484 has a brief section on distributing typing information. In this section [2]_ the PEP recommends using ``shared/typehints/pythonX.Y/`` for shipping stub files. However, manually adding a path to stub files for each third party library does not scale. The simplest approach people have taken is to add ``site-packages`` to their ``MYPYPATH``, but this causes type checkers to fail on packages that are highly dynamic (e.g. sqlalchemy and Django). Specification ============= There are several motivations and methods of supporting typing in a package. This PEP recognizes three (3) types of packages that may be created: 1. The package maintainer would like to add type information inline. 2. The package maintainer would like to add type information via stubs. 3. A third party would like to share stub files for a package, but the maintainer does not want to include them in the source of the package. This PEP aims to support these scenarios and make them simple to add to packaging and deployment. The two major parts of this specification are the packaging specifications and the resolution order for resolving module type information. This spec is meant to replace the ``shared/typehints/pythonX.Y/`` spec of PEP 484 [2]_. New third party stub libraries are encouraged to distribute stubs via the third party packaging proposed in this PEP in place of being added to typeshed. Typeshed will remain in use, but if maintainers are found, third party stubs in typeshed are encouraged to be split into their own package. Packaging Type Information -------------------------- Packages must opt into supporting typing. This will be done though a distutils extension [3]_, providing a ``typed`` keyword argument to the distutils ``setup()`` command. The argument value will depend on the kind of type information the package provides. The new keyword will be added to Python 3.7 and will also be accessible in the ``typing_extensions`` package though a distutils extension. This enables a package maintainer to write :: setup( ... setup_requires=["typing_extensions"], typed="inline", ... ) Inline Typed Packages ''''''''''''''''''''' Packages that have inline type annotations simply have to pass the value ``"inline"`` to the ``typed`` argument in ``setup()``. Stub Only Packages '''''''''''''''''' For package maintainers wishing to ship stub files containing all of their type information, it is prefered that the ``*.pyi`` stubs are alongside the corresponding ``*.py`` files. However, the stubs may be put in a sub-folder of the Python sources, with the same name the ``*.py`` files are in. For example, the ``flyingcircus`` package would have its stubs in the folder ``flyingcircus/flyingcircus/``. This path is chosen so that if stubs are not found in ``flyingcircus/`` the type checker may treat the subdirectory as a normal package. The normal resolution order of checking ``*.pyi`` before ``*.py`` will be maintained. The value of the ``typed`` argument to ``setup()`` is ``"stubs"`` for this type of distribution. The author of the package is suggested to use ``package_data`` to assure the stub files are installed alongside the runtime Python code. Third Party Stub Packages ''''''''''''''''''''''''' Third parties seeking to distribute stub files are encouraged to contact the maintainer of the package about distribution alongside the package. If the maintainer does not wish to maintain or package stub files or type information inline, then a "third party stub package" should be created. The structure is similar, but slightly different from that of stub only packages. If the stubs are for the library ``flyingcircus`` then the package should be named ``flyingcircus-stubs`` and the stub files should be put in a sub-directory named ``flyingcircus``. This allows the stubs to be checked as if they were in a regular package. These packages should also pass ``"stubs"`` as the value of ``typed`` argument in ``setup()``. These packages are suggested to use ``package_data`` to package stub files. In addition, the package should indicate which version(s) of the runtime package are supported via the ``install_requires`` argument to ``setup()``. Type Checker Module Resolution Order ------------------------------------ The following is the order that type checkers supporting this PEP should resolve modules containing type information: 1. User code - the files the type checker is running on. 2. Stubs or Python source manually put in the beginning of the path. Type checkers should provide this to allow the user complete control of which stubs to use, and patch broken stubs/inline types from packages. 3. Third party stub packages - these packages can supersede the installed untyped packages. They can be found at ``pkg-stubs`` for package ``pkg``, however it is encouraged to check their metadata to confirm that they opt into type checking via the ``typed`` keyword. 4. Inline packages - finally, if there is nothing overriding the installed package, and it opts into type checking. 5. Typeshed (if used) - Provides the stdlib types and several third party libraries When resolving step (3) type checkers should assure the version of the stubs is compatible with the installed runtime package through the method described above. Type checkers that check a different Python version than the version they run on must find the type information in the ``site-packages``/``dist-packages`` of that Python version. This can be queried e.g. ``pythonX.Y -c 'import sys; print(sys.exec_prefix)'``. It is also recommended that the type checker allow for the user to point to a particular Python binary, in case it is not in the path. To check if a package has opted into type checking, type checkers are recommended to use the ``pkg_resources`` module to query the package metadata. If the ``typed`` package metadata has ``None`` as its value, the package has not opted into type checking, and the type checker should skip that package. References ========== .. [1] Typeshed (https://github.com/python/typeshed) .. [2] PEP 484, Storing and Distributing Stub Files (https://www.python.org/dev/peps/pep-0484/#storing-and-distributing-stub-file...) .. [3] Distutils Extensions, Adding setup() arguments (http://setuptools.readthedocs.io/en/latest/setuptools.html#adding-setup-argu...) Copyright ========= This document has been placed in the public domain.  .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 coding: utf-8 End: