title: What is the use of stub files (.pyi ) in python?
body: <p>I am trying to understand the lower level implementations of python 3. There is one module named <strong>_posixsubprocess</strong> used by the <a href="https://github.com/python/cpython/blob/8184f0fce3b734413e3d3a282f1425d3cb8507fd/Lib/subprocess.py" rel="nofollow noreferrer">subprocess module</a>. I tried to find the location of this module in my system and found that it's a stub file.</p>
  <p>Could someone guide me as I have no idea about what are the stub files and how are they implemented at the lower level?</p>