Python Cookbook 2Nd Edition Jun 1002005 [Electronic resources] نسخه متنی

Recipe 2.17. Swapping One File Extension for Another Throughout a Directory Tree

Credit: Julius Welby

Problem

You need to rename files throughout a
subtree of directories, specifically changing the names of all files
with a given extension so that they have a different extension
instead.

Solution

Operating on all files of a whole subtree of directories is easy
enough with the os.walk function from
Python's standard library:

import os
def swapextensions(dir, before, after):
if before[:1] != '.':
before = '.'+before
thelen = -len(before)
if after[:1] != '.':
after = '.'+after
for path, subdirs, files in os.walk(dir):
for oldfile in files:
if oldfile[thelen:] == before:
oldfile = os.path.join(path, oldfile)
newfile = oldfile[:thelen] + after
os.rename(oldfile, newfile)
if _ _name_ _=='_ _main_ _':
import sys
if len(sys.argv) != 4:
print "Usage: swapext rootdir before after"
sys.exit(100)
swapextensions(sys.argv[1], sys.argv[2], sys.argv[3])

Discussion

This recipe shows how to change the file extensions of all files in a
specified directory, all of its subdirectories, all of
their subdirectories, and so on. This technique
is useful for changing the extensions of a whole batch of files in a
folder structure, such as a web site. You can also use it to correct
errors made when saving a batch of files programmatically.

The recipe is usable either as a module to be imported from any
other, or as a script to run from the command line, and it is
carefully coded to be platform-independent. You can pass in the
extensions either with or without the leading dot (.), since the code
in this recipe inserts that dot, if necessary. (As a consequence of
this convenience, however, this recipe is unable to deal with files
completely lacking any extension, including the dot; this limitation
may be bothersome on Unix systems.)

The implementation of this recipe uses techniques that purists might
consider too low levelspecifically by dealing mostly with
filenames and extensions by direct string manipulation, rather than
by the functions in module os.path.
It's not a big deal: using
os.path is fine, but using
Python's powerful string facilities to deal with
filenames is fine, too.

See Also

The author's web page at http://www.outwardlynormal.com/python/swapextensions.