What does "i" represent in Python .pyi extension?

In Python, what does "i" represent in .pyi extension?

In [PEP-484][1], it mentions .pyi is "a stub file" but no mnemonic help on the extension. So does the "i" mean "Include"? "Implementation"? "Interface"?

[1]: https://www.python.org/dev/peps/pep-0484/ "PEP-484" [2]: https://stackoverflow.com/users/8922283/pyprohly [3]: https://stackoverflow.com/a/62881746/2088339 [4]: https://stackoverflow.com/users/4530440/kruup%c3%b6s [5]: https://stackoverflow.com/a/45440199/2088339

I think the i in .pyi stands for "Interface"

Definition for Interface in Java:

> An interface in the Java programming language is an abstract type that > is used to specify a behaviour that classes must implement

• From Python typeshed github repository:

> Each Python module is represented by a .pyi "stub". This is a normal > Python file (i.e., it can be interpreted by Python 3), except all the > methods are empty.

• In 'Mypy' repository, they explicitly mention "stub" files as public interfaces:

> A stubs file only contains a description of the public interface of > the module without any implementations.

Because "Interfaces" do not exist in Python (see this SO question between Abstract class and Interface) I think the designers intended to dedicate a special extension for it.

pyi implements "stub" file (definition from Martin Fowler)

> Stubs: provide canned answers to calls made during the test, usually > not responding at all to anything outside what's programmed in for the > test.

But people are more familiar with Interfaces than "stub" files, therefore it was easier to choose .pyi rather than .pys to avoid unnecessary confusion.

Apparently PyCharm creates .pyi file for its own purposes:

>The *.pyi files are used by PyCharm and other development tools to provide more information, such as PEP 484 type hints, than it is able to glean from introspection of extension types and methods. They are not intended to be imported, executed or used for any other purpose other than providing info to the tools. If you don't use use a tool that makes use of .pyi files then you can safely ignore this file.

>See: https://www.python.org/dev/peps/pep-0484/ https://www.jetbrains.com/help/pycharm/2016.1/type-hinting-in-pycharm.html

This comment was found in: python27/Lib/site-packages/wx/core.pyi

The i in .pyi stands for ‘interface’.

The .pyi extension was first mentioned in this GitHub issue thread where JukkaL says:

> I'd probably prefer an extension with just a single dot. It also needs to be something that is not in use (it should not be used by cython, etc.). .pys seems to be used in Windows (or was). Maybe .pyi, where i stands for an interface definition?

Another way to explain the contents of a module that Wing can't figure out is with a pyi Python Interface file. This file is merely a Python skeleton with the proper structure, call signature, and return values to correspond to the functions, attributes, classes, and methods specified in a module.