Question

Consider the following:

>>> from django.conf import settings
>>> import os
>>> settings.VIRTUAL_ENV
'C:/Users/Marcin/Documents/oneclickcos'
>>> settings.EXTRA_BASE
'/oneclickcos/'
>>> os.path.join(settings.VIRTUAL_ENV,settings.EXTRA_BASE)
'/oneclickcos/'

As you can imagine, I neither expect nor want the concatenation of 'C:/Users/Marcin/Documents/oneclickcos' and '/oneclickcos/' to be '/oneclickcos/'.

Oddly enough, reversing the path components once again shows python ignoring the first path component:

>>> os.path.join(settings.EXTRA_BASE,settings.VIRTUAL_ENV)
'C:/Users/Marcin/Documents/oneclickcos'

While this works something like expected:

>>> os.path.join('/foobar',settings.VIRTUAL_ENV,'barfoo')
'C:/Users/Marcin/Documents/oneclickcos\\barfoo'

I am of course, running on Windows (Windows 7), with the native python.

Why is this happening, and what can I do about it?

Answer 1

That’s pretty much how os.path.join is defined (quoting the docs):

If any component is an absolute path, all previous components (on Windows, including the previous drive letter, if there was one) are thrown away

And I’d say it’s usually a good thing, as it avoids creating invalid paths. If you want to avoid this behavior, don’t feed it absolute paths. Yes, starting with a slash qualifies as absolute path. A quick and dirty solution is just removing the leading slash (settings.EXTRA_BASE.lstrip('/') if you want to do it programmatically).