Python splitext

Question

In python, why is os.path.splitext using '.' as extension separator instead of os.extsep?

Answer 1

os.extsep is defined by importing os.path.extsep. But you're right, os.path.splitext() always uses ., regardless of os.path.extsep:

From os.py (3.2.2):

from os.path import (curdir, pardir, sep, pathsep, defpath, extsep, altsep,
    devnull)

From ntpath.py (which becomes os.path)

extsep = '.'
[...]
def _get_dot(path):
    if isinstance(path, bytes):
        return b'.'
    else:
        return '.'   # instead of return extsep! [Comment by me, not in source]
[...]
def splitext(p):
    return genericpath._splitext(p, _get_sep(p), _get_altsep(p),
                                 _get_dot(p))

Also, from genericpath.py:

def _get_dot(path):
    if isinstance(path, bytes):
        return b'.'
    else:
        return '.'

So os.path() does in fact define the extension separator twice.

Now it probably doesn't matter because it's not going to change anytime soon (it's the same on all supported platforms anyway). But in a way, it violates the DRY principle.