What is the use of Python's basic optimizations mode? (python -O)

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

Another use for the -O flag is that the value of the __debug__ builtin variable is set to False.

So, basically, your code can have a lot of "debugging" paths like:

if __debug__:
     # output all your favourite debugging information
     # and then more

which, when running under -O, won't even be included as bytecode in the .pyo file; a poor man's C-ish #ifdef.

Remember that docstrings are being dropped only when the flag is -OO.