Purpose: | Cache directory listings, updating when the modification time of a directory changes. |
---|---|
Python Version: | 1.4 and later |
The main function in the dircache API is listdir(), a wrapper around os.listdir() that caches the results and returns the same list each time it is called with the a path unless the modification date of the named directory changes.
import dircache
path = '.'
first = dircache.listdir(path)
second = dircache.listdir(path)
print 'Contents :', first
print 'Identical:', first is second
print 'Equal :', first == second
It is important to recognize that the exact same list is returned each time, so it should not be modified in place.
$ python dircache_listdir.py
Contents : ['.svn', '__init__.py', 'dircache_annotate.py', 'dircache_listdir.py',
'dircache_listdir_file_added.py', 'dircache_reset.py']
Identical: True
Equal : True
Of course, if the contents of the directory changes it is rescanned.
import dircache
import os
path = '/tmp'
file_to_create = os.path.join(path, 'pymotw_tmp.txt')
# Look at the directory contents
first = dircache.listdir(path)
# Create the new file
open(file_to_create, 'wt').close()
# Rescan the directory
second = dircache.listdir(path)
# Remove the file we created
os.unlink(file_to_create)
print 'Identical :', first is second
print 'Equal :', first == second
print 'Difference:', list(set(second) - set(first))
In this case the new file causes a new list to be constructed.
$ python dircache_listdir_file_added.py
Identical : False
Equal : False
Difference: ['pymotw_tmp.txt']
It is also possible to reset the entire cache, discarding its contents so that each path will be rechecked.
import dircache
path = '/tmp'
first = dircache.listdir(path)
dircache.reset()
second = dircache.listdir(path)
print 'Identical :', first is second
print 'Equal :', first == second
print 'Difference:', list(set(second) - set(first))
$ python dircache_reset.py
Identical : False
Equal : True
Difference: []
The other interesting function provided by the dircache module is annotate(). When called, annotate() modifies a list such as is returned by listdir(), adding a ‘/’ to the end of the names that represent directories. (Sorry Windows users, although it uses os.path.join() to construct names to test, it always appends a ‘/’, not os.sep.)
import dircache
from pprint import pprint
path = '../../trunk'
contents = dircache.listdir(path)
annotated = contents[:]
dircache.annotate(path, annotated)
fmt = '%20s\t%20s'
print fmt % ('ORIGINAL', 'ANNOTATED')
print fmt % (('-' * 20,)*2)
for o, a in zip(contents, annotated):
print fmt % (o, a)
$ python dircache_annotate.py
ORIGINAL ANNOTATED
-------------------- --------------------
.DS_Store .DS_Store
.svn .svn/
ChangeLog ChangeLog
LICENSE.txt LICENSE.txt
MANIFEST MANIFEST
MANIFEST.in MANIFEST.in
MANIFEST.in.in MANIFEST.in.in
Makefile Makefile
PyMOTW PyMOTW/
README.txt README.txt
setup.py.in setup.py.in
static_content static_content/
template.html template.html
See also