File with a .PY extension contains source code of a program or a script stored in the object-oriented, interpreted programming language Python. In order to initiate PY files, a language interpreter is required. Such interpreter is provided either by the programming environment in which they are created or separately, if they are created in the simple text editors or downloaded from different sources.

Python is an open-source language, designed in order to provide an easy readout and implementation. It is often used to implement servers or administrated computer systems, and also many other applications, commercial and free.