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

Recipe 2.9. Reading Data from zip Files

Credit: Paul Prescod, Alex Martelli

Problem

You want to directly examine some or all
of the files contained in an archive in zip
format, without expanding them on disk.

Solution

zip files are a popular, cross-platform way of
archiving files. The Python Standard Library comes with a
zipfile module to access such files
easily:

import zipfile
z = zipfile.ZipFile("zipfile.zip", "r")
for filename in z.namelist( ):
print 'File:', filename,
bytes = z.read(filename)
print 'has', len(bytes), 'bytes'

Discussion

Python can work directly with data in zip files.
You can look at the list of items in the archive's
directory and work with the "data
file"s themselves. This recipe is a snippet that
lists all of the names and content lengths of the files included in
the zip archive
zipfile.zip.

The zipfile module does not currently handle
multidisk zip files nor zip
files with appended comments. Take care to use
r as the flag argument, not
rb, which might seem more natural (e.g.,
on Windows). With ZipFile, the flag is not used
the same way when opening a file, and rb
is not recognized. The r flag handles the
inherently binary nature of all zip files on all
platforms.

When a zip file contains some Python modules
(meaning .py or preferably
.pyc files), possibly in addition to other
(data) files, you can add the file's path to
Python's sys.path and then use
the import statement to import modules from the
zip file. Here's a toy,
self-contained, purely demonstrative example that creates such a
zip file on the fly, imports a module from it,
then removes itall just to show you how it's
done:

import zipfile, tempfile, os, sys
handle, filename = tempfile.mkstemp('.zip')
os.close(handle)
z = zipfile.ZipFile(filename, 'w')
z.writestr('hello.py', 'def f( ):
 return "hello world from "+_ _file_ _\n')
z.close( )
sys.path.insert(0, filename)
import hello
print hello.f( )
os.unlink(filename)

Running this script emits something like:

hello world from /tmp/tmpESVzeY.zip/hello.py

Besides illustrating
Python's ability to import from a
zip file, this snippet also shows how to make
(and later remove) a temporary file, and how to use the
writestr method to add a member to a
zip file without placing that member into a disk
file first.

Note that the path to the zip file from which
you import is treated somewhat like a directory.
(In this specific example run, that path is
/tmp/tmpESVzeY.zip, but of course, since
we're dealing with a temporary file, the exact value
of the path can change at each run, depending also on your platform.)
In particular, the _ _file_ _ global variable,
within the module hello, which is
imported from the zip file,
has a value of
/tmp/tmpESVzeY.zip/hello.pya
pseudo-path, made up of the
zip file's path seen as a
"directory" followed by the
relative path of hello.py within the
zip file. If you import from a
zip file a module that computes paths relative
to itself in order to get to data files, you need to adapt the module
to this effect, because you cannot just open such
a "pseudo-path" to get a file
object: rather, to read or write files inside a
zip file, you must use functions from standard
library module zipfile, as shown in the solution.

For more information about importing modules from a
zip file, see Recipe 16.12. While that recipe is
Unix-specific, the information in the recipe's
Discussion about importing from zip files is
also valid for Windows.

See Also

Documentation for the zipfile module in the
Library Reference and Python in a
Nutshell; modules tempfile,
os, sys; for archiving a tree
of files, see Recipe 2.11;
for more information about importing modules from a
zip file, Recipe 16.12.