[Python-ideas] os.path.isparent and os.path.ischild

[Steven D'Aprano]

Andrew Bennetts wrote:
> Steven D'Aprano wrote:
>> I'm not sure that this is so common and useful that it needs to be
>> included in os.path. You can always just add it to your own library,
>> or even write them in-line: the implementation is just a one-liner.
>>
>> def isparent(path1, path2):
>>     "Returns True if path1 is a parent of path2."
>>     return os.path.commonprefix([path1, path2]) == path1
>>
>> def ischild(path1, path2):
>>     "Returns True if path1 is a child of path2."
>>     return os.path.commonprefix([path1, path2]) == path2
> 
> Those one-liners are simple, obvious, and dangerously wrong:
> 
>>>> ischild('aa', 'a')
> True

I would call that a bug in commonprefix.

 >>> os.path.commonprefix(['/dir/pics/file', '/dir/pictures/file'])
'/dir/pic'


commonprefix is documented as returning the longest common path 
component, not leading substring:

 >>> help(os.path.commonprefix)

commonprefix(m)
     Given a list of pathnames, returns the longest common leading
     component



-- 
Steven