how to get os.py to use an ./ntpath.py instead of Lib/ntpath.py

[Steven D'Aprano]

On Mon, 10 Sep 2012 10:25:29 -0700, ruck wrote:

> In Python 2.7.2 on Windows 7,
> 
> os.walk() uses isdir(),
> which comes from os.path,
> which really comes from ntpath.py,
> which really comes from genericpath.py
> 
> I want os.walk() to use a modified isdir() on my Windows 7. Not knowing
> any better, it seems to me like ntpath.py would be a good place to
> intercept.
> 
> When os.py does "import ntpath as path", how can I get python to process
> my customized ntpath.py instead of Lib/ntpath.py ?

import os
os.path.isdir = my_isdir

ought to do it.

This general technique is called "monkey-patching". The Ruby community is 
addicted to it. Everybody else -- and a goodly number of the more 
sensible Ruby crowd -- consider it a risky, dirty hack that 99 times out 
of 100 will lead to blindness, moral degeneracy and subtle, hard-to-fix 
bugs.

They are right to be suspicious of it. As a general rule, monkey-patching 
is not for production code. You have been warned.

http://www.codinghorror.com/blog/2008/07/monkeypatching-for-humans.html


[...]
> Why?  Because the genericpath implementation relies on os.stat() which
> uses Windows API function that presumes or enforces some naming
> conventions like "doesn't end with a space or a period". But the NTFS
> actually supports such filenames and dirnames, and some sw (like cygwin)
> lets users make files & dirs without restricting. So, cygwin users like
> me may have file 'voo...\\doo' which os.walk() cannot ordinarily walk. 
> That is, the isdir('voo...') returns false because the underlying
> os.stat is assessing 'voo' instead of 'voo...' . 

Please consider submitting a patch that adds support for cygwin paths to 
the standard library. You'll need to target 3.4 though, 2.7 is now a 
maintenance release with no new features allowed.


> The workaround is to
> pass os.stat a fullpathname that is prefixed with r'\\?\' so the Windows
> API recognizes that you do NOT want the name filtered.
> 
> Better said by Microsoft:
> "For file I/O, the "\\?\" prefix to a path string tells the Windows APIs
> to disable all string parsing and to send the string that follows it
> straight to the file system.

That's not so much a workaround as the officially supported API for 
dealing with the situation you are in. Why don't you just prepend a '?' 
to paths like they tell you to?


-- 
Steven