Question :
What does Python optimization (-O or PYTHONOPTIMIZE) do?
The docs only say that Python interpreter performs “basic optimizations”, without going into any detail. Obviously, it’s implementation dependent, but is there any way to get a feel for what type of things could be optimized, and how much run-time savings it could generate?
Is there any downside to using -O?
The only thing I know is that -O disables assert, but presumably one shouldn’t use assert for things that could still go wrong in production.
Answer #1:
In Python 2.7, -O has the following effect:
- the byte code extension changes to
.pyo - sys.flags.optimize gets set to 1
__debug__is False- asserts don’t get executed
In addition -OO has the following effect:
- sys.flags.optimize gets set to 2
- doc strings are not available
To verify the effect for a different release of CPython, grep the source code for Py_OptimizeFlag.
Link to official documentation: https://docs.python.org/2.7/tutorial/modules.html#compiled-python-files
