Joe Ardent wrote:
> Good day, everybody! From what I can tell from the archives, this is
> everyone's favorite method from the standard lib, and everyone loves
> answering questions about it. Right? :)
I don't know what to make of the smiley, so I'll be explicit: use os.walk()
instead of os.path.walk().
> Anyway, my question regards the way that the visit callback modifies
> the names list. Basically, my simple example is:
>
> ##############################
> def listUndottedDirs( d ):
> dots = re.compile( '\.' )
>
> def visit( arg, dirname, names ):
> for f in names:
> if dots.match( f ):
> i = names.index( f )
> del names[i]
> else:
> print "%s: %s" % ( dirname, f )
>
> os.path.walk( d, visit, None )
> ###############################
>
> Basically, I don't want to visit any hidden subdirs (this is a unix
> system), nor am I interested in dot-files. If I call the function
> like, "listUndottedDirs( '/usr/home/ardent' )", however, EVEN THOUGH
> IT IS REMOVING DOTTED DIRS AND FILES FROM names, it will recurse into
> the dotted directories; eg, if I have ".kde3/" in that directory, it
> will begin listing the contents of /usr/home/ardent/.kde3/ . Here's
> what the documentation says about this method:
>
> "The visit function may modify names to influence the set of
> directories visited below dirname, e.g. to avoid visiting certain
> parts of the tree. (The object referred to by names must be modified
> in place, using del or slice assignment.)"
>
> So... What am I missing? Any help would be greatly appreciated.
Your problem is that you are deleting items from a list while iterating over
it:
# WRONG
>>> names = [".alpha", ".beta", "gamma"]
>>> for name in names:
... if name.startswith("."):
... del names[names.index(name)]
...
>>> names
['.beta', 'gamma']
Here's one way to avoid that mess:
>>> names = [".alpha", ".beta", "gamma"]
>>> names[:] = [name for name in names if not name.startswith(".")]
>>> names
['gamma']
The slice [:] on the left side is necessary to change the list in-place.
Peter
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