.py File Extension

What kind of file is a .py?

A .py file contains Python source code. It may be a script you run directly, an importable module, or one piece of a larger package. The widely used text/x-python MIME type describes these files, although it is not registered with IANA and some systems label them text/plain instead.¹

Python source has no dependable magic number. An optional first line such as #!/usr/bin/env python3 can identify an interpreter on Unix-like systems, but the filename, media type, and readable contents are stronger clues when considered together.

Python 3 treats source as UTF-8 by default. A specially formatted comment on the first or second line can declare another character encoding for the whole file.²

How do I open a .py on my computer?

Any text editor can open a .py file on Windows, macOS, or Linux. A Python-aware editor is more useful because Python indentation affects program structure.

• Visual Studio Code provides completion, navigation, linting, testing, and debugging when its Python extension and a Python interpreter are installed.³
• PyCharm provides Python-focused code analysis, interpreter setup, testing, and debugging.⁴
• Python can run a trusted file from a terminal with python path/to/script.py.⁵

Opening a file for inspection is different from executing it. Review unfamiliar scripts first. Python code can modify files, read credentials, start processes, access networks, and import more code.

Poly support for .py

Poly opens .py source in a code-friendly editor with Python syntax highlighting, word wrap, and in-file search. It indexes readable source for exact and semantic search, so you can find a known identifier or search by what the code does.

The Poly agent can summarize functions and classes, explain visible control flow, and help reason about changes. Poly does not execute the program. Runtime state, environment variables, generated code, network responses, and dependencies are available only when you provide the relevant material.

History of .py

Guido van Rossum started work on Python in December 1989 as a successor to ABC. He chose the name as a reference to Monty Python's Flying Circus, not the snake.⁶ Python's first public release followed in 1991.

The .py suffix became the conventional marker for Python source as the language spread across Unix, Windows, and macOS tools. The freedesktop.org shared MIME database associates both .py and .wsgi with text/x-python and also uses interpreter lines as supporting evidence.¹

Working with .py and alternatives

Keep .py when people need portable, reviewable source. Save it as UTF-8 unless a project has a specific legacy requirement, and preserve the encoding declaration when one is necessary.

Choose another format only when the workflow calls for it:

Changing .py to another suffix does not translate the program. Conversion must preserve valid Python syntax, source encoding, dependencies, and any required interpreter version.