What does i represent in Python .pyi extension?

What does i represent in Python .pyi extension?

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 whats programmed in for the

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 dont 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/

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

What does i represent in Python .pyi extension?

The i in .pyi stands for ‘interface’.

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

Id 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?

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