What is the use of Python's basic optimization

Question

Python has a flag -O that you can execute the interpreter with. The option will generate "optimized" bytecode (written to .pyo files), and given twice, it will discard docstrings. From Python's man page:

-O Turn on basic optimizations. This changes the filename extension for compiled (bytecode) files from .pyc to .pyo. Given twice, causes docstrings to be discarded.

This option's two major features as I see it are:

• Strip all assert statements. This trades defense against corrupt program state for speed. But don't you need a ton of assert statements for this to make a difference? Do you have any code where this is worthwhile (and sane?)

• Strip all docstrings. In what application is the memory usage so critical, that this is a win? Why not push everything into modules written in C?

What is the use of this option? Does it have a real-world value?

Answer 1

If you have assertions in frequently called code (e.g. in an inner loop), stripping them can certainly make a difference. Extreme example:

$ python    -c 'import timeit;print timeit.repeat("assert True")'
[0.088717937469482422, 0.088625192642211914, 0.088654994964599609]
$ python -O -c 'import timeit;print timeit.repeat("assert True")'
[0.029736995697021484, 0.029587030410766602, 0.029623985290527344]

In real scenarios, savings will usually be much less.

Stripping the docstrings might reduce the size of your code, and hence your working set.

In many cases, the performance impact will be negligible, but as always with optimizations, the only way to be sure is to measure.