What do the Python file extensions, .pyc .pyd .pyo stand for?

Distinguishing Python file types

Python file extensions dictate how the interpreter processes and interacts with your files. They can affect performance, speed, and functionality. Let's delve deeper into their specific roles:

*.pyc—The Performance Booster

A .pyc is generated by the Python interpreter when you import a .py file. It contains bytecode—a lower-level, platform-independent version of your source code. These files are created in a __pycache__ directory and their aim is to accelerate startup on subsequent runs by bypassing the initial compilation stage.

*.pyo—The Optimization Attempt

.pyo files were created by running Python with the -O flag and contained optimized bytecode. The core "optimization" was the removal of assert statements, and they were used in Python versions prior to 3.5. However, their potential for causing unpredictable behavior led to their deprecation.

*.pyd—Bridging Python and C

A .pyd file is a Python Dynamic module (Python's DLL or Dynamic Link Library) on Windows. Python import statements can import these modules just like regular Python modules. They are typically C or C++ extensions that add ledgehammer power to Python programs. Linux systems recognize these files under the .so extension.

Nuts & Bolts of Python File Extensions

Script or Module—Where's my *.pyc?

A *.pyc or *.pyo file isn't created when the script is simply being executed as the principal program. These files appear when modules are incorporated in a Python session to boost the module loading times.

Guest appearances: .pyw and .pyx

On the periphery, we've got *.pyw files that are Python scripts running sans console window, designed for Windows GUI programs. For those dabbling in advanced Python extensions, *.pyx files are from Cython, facilitating interfaces with C/C++ code for creating extension modules.

The Need for Speed

Bytecode files such as *.pyc can load up to 3 times faster than their initial *.py counterparts. This significant speed bump improves startup times for your frequently-run applications.

Aladdin's cave—Unofficial Extensions

Across your Python adventures, you may stumble upon rare and unofficial Python file extensions. Information on tools like PyInstaller (for generating executables) or PyOxidizer (for packaging applications) can reveal unique facets of Python's flexible ecosystem. Remember: a shiny new extension might be your magic lamp.