Project:Python/Byte compiling

Levels of optimization
Python generally supports three levels of optimization:
 * non-optimized code (.pyc),
 * code without debug statements (.pyo, .opt-1.pyc),
 * code without debug and docstrings (.pyo, .opt-2.pyc).

The use of optimization on compiled byte-code depends on implementation:
 * all implementations use plain .pyc for non-optimized code,
 * PyPy2.7 does not write optimized code to byte-code files,
 * Python 2.7 uses .pyo for both levels of optimization, i.e. you can choose only one level and it'll stay,
 * Python 3.5+ and PyPy3.5+ use .opt-1.pyc and .opt-2.pyc for the optimized code.

How to byte-compile Python modules?
Generally, byte-compiling is done via importing the module with appropriate Python optimization flags. Python provides a convenience compileall module to do that for all modules in a directory.

The reference code to perform complete byte-compilation is:

Note that -d should specify the 'live system' path to the compiled directory, while the position argument takes current (i.e. DESTDIR) path to it.

The first (non-optimized) variant applies to all Python implementations. -OO is done on all but PyPy2.7, -O is done on implementations using separate suffixes for optimization levels (Python3.5+ / PyPy3.5+). Generally, it should be fine to call more variants than necessary but it might be a waste of CPU cycles.