Behaviour of os.path.join

[BlindAnagram]

On 27/05/2020 16:53, Ben Bacarisse wrote:
> BlindAnagram <blindanagram at nowhere.com> writes:
> 
>> On 27/05/2020 13:30, Ben Bacarisse wrote:
>>> BlindAnagram <blindanagram at nowhere.com> writes:
>>>
>>>> The issue that I raised here was whether the behaviour of os.path.join()
>>>> in treating the Windows directory separator '\\' as an absolute path
>>>> should be considered a bug.
>>>
>>> You think it should be considered to be a relative path?  The only
>>> meaning that would give you want you wanted from
>>>
>>>   os.path.join(<something>, '\\')
>>>
>>> would be to treat it as being relative to the drive and to the
>>> directory.  In other words you want '\\' to be a synonym for '.'  The
>>> usual meaning of '\\' (outside of this specific function) is "root on
>>> the current drive" but that can't sensibly be appended to any path.
>>>
>>>> The behaviour of join came up for me when I tried to use the os.path
>>>> functions to create a path that could only ever be used as a directory
>>>> and never a file.  The only way that I found to designate a path as a
>>>> directory path was to add '\\' at the end.  But this doesn't work in
>>>> using os.path becaause the other os.path functions just strip it off and
>>>> turn the directories back into files.
>>>
>>> Nothing about the name can turn a directory into a file (or vice versa).
>>> If c:\x\y is a file, calling it c:\x\y\ won't change that, but it might
>>> give you an error when you try to access it.  That may be what you want.
>>> If so, appending '.' is likely to be more portable.
>>
>> That is true if you know for sure how your path will be used.
>>
>> But if you don't, there is a world of difference between passing the
>> paths 'name' and 'name\\' on for others to use. And in this situation it
>> doesn't help when os.path functions strip the directory separator off.
> 
> As it should.  Relying on a trailing \ having the right effect is
> brittle to say the least.

In my case less brittle than leaving it out.  I don't want to bore
people with the details but the convention on the target system is that
directory paths must always end with '\\' into order to be interpreted
as directories.  Its not my choice but I see this as a perfectly
reasonable convention. Obviously others may disagree.

>> This situation resulted in a bug that was surprisingly hard to track
>> down because it created hidden files instead of directories as
>> intended.
> 
> If so, the bug is not in os.path.join and trying to fix it by insisting
> that a path have trailing \ may well just stacking up more problems for
> later.
> 
>> After finding and correcting the '\\' that had been stripped off, the
>> desired directories couldn't then be creaated on the target because
>> hidden files were present with these names.
> 
> As I said, that's a dodgy thing to rely on.  It may be that you can't
> fix the bug any other way (some aspect of the overall design may be
> broken), but I would urge you to try.

Its not my bug to fix - the semantics of what I send is very clear on
any Windows system.