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

[Thomas Rachel]

Am 11.09.2012 05:46 schrieb Steven D'Aprano:

> Good for you. (Sorry, that comes across as more condescending than it is
> intended as.) Monkey-patching often gets used for quick scripts and tiny
> pieces of code because it works.
>
> Just beware that if you extend that technique to larger bodies of code,
> say when using a large framework, or multiple libraries, your experience
> may not be quite so good. Especially if *they* are monkey-patching too,
> as some very large frameworks sometimes do. (Or so I am lead to believe.)

This sonds like a good use case for a context manager, like the one in 
decimal.Context.get_manager().

First shot:

@contextlib.contextmanager
def changed_os_path(**k):
     old = {}
     try:
         for i in k.items():
             old[i] = getattr(os.path, i)
             setattr(os.path, i, k[i])
         yield None
     finally:
         for i in k.items():
             setattr(os.path, i, old[i])

and so for your code you can use

     print 'os.walk(\'goo\') with modified isdir()'
     with changed_os_path(isdir=my_isdir):
         for root, dirs, files in os.walk('goo'):
             print root, dirs, files

so the change is only effective as long as you are in the relevant code 
part and is reverted as soon as you leave it.


Thomas