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example-walking-iso-filesystem.md

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Example: Walking the ISO filesystem

In some circumstances it may be useful to walk all or some of the filesystem tree on the ISO. For that purpose, PyCdlib provides the walk API. Much like the built-in Python os.walk API, this method takes a PyCdlib full path, and iterates over the entire filesystem starting at that root. For each directory, the method returns a 3-tuple of (dirpath, dirnames, filenames) that can be used by the user. Here's the complete code for this example:

try:
    from cStringIO import StringIO as BytesIO
except ImportError:
    from io import BytesIO

import pycdlib

iso = pycdlib.PyCdlib()
iso.new()

iso.add_directory('/DIR1')
foostr = b'foo\n'
iso.add_fp(BytesIO(foostr), len(foostr), '/DIR1/FOO.;1')
barstr = b'bar\n'
iso.add_fp(BytesIO(barstr), len(barstr), '/DIR1/BAR.;1')
iso.add_directory('/DIR2')
bazstr = b'baz\n'
iso.add_fp(BytesIO(bazstr), len(bazstr), '/DIR2/BAZ.;1')

for dirname, dirlist, filelist in iso.walk(iso_path='/'):
    print("Dirname:", dirname, ", Dirlist:", dirlist, ", Filelist:", filelist)

for dirname, dirlist, filelist in iso.walk(iso_path='/DIR1'):
    print("Dirname:", dirname, ", Dirlist:", dirlist, ", Filelist:", filelist)

iso.close()

Let's take a closer look at the code.

try:
    from cStringIO import StringIO as BytesIO
except ImportError:
    from io import BytesIO

import pycdlib

As in earlier examples, import the relevant libraries, including pycdlib itself.

iso = pycdlib.PyCdlib()
iso.new()

Create a new PyCdlib object, and then create a new ISO with that object.

iso.add_directory('/DIR1')
foostr = b'foo\n'
iso.add_fp(BytesIO(foostr), len(foostr), '/DIR1/FOO.;1')
barstr = b'bar\n'
iso.add_fp(BytesIO(barstr), len(barstr), '/DIR1/BAR.;1')
iso.add_directory('/DIR2')
bazstr = b'baz\n'
iso.add_fp(BytesIO(bazstr), len(bazstr), '/DIR2/BAZ.;1')

As in earlier examples, create some new directories and files on the ISO from strings.

for dirname, dirlist, filelist in iso.walk(iso_path='/'):
    print("Dirname:", dirname, ", Dirlist:", dirlist, ", Filelist:", filelist)

Use the walk API to iterate over the directories and files on the ISO, printing them out in turn. Note that walk takes one and only one of iso_path, rr_path, joliet_path, or udf_path, and only accepts rr_path, joliet_path, or udf_path if the ISO supports those extensions. Since we added a number of files and directories on the ISO, the above code will print out:

Dirname: / , Dirlist: ['DIR2', 'DIR1'] , Filelist: []
Dirname: /DIR1 , Dirlist: [] , Filelist: ['FOO.;1', 'BAR.;1']
Dirname: /DIR2 , Dirlist: [] , Filelist: ['BAZ.;1']

This can be interpreted as follows. The "dirname" is the name of the directory currently being examined; for the root it is /, while it is /DIR1 and /DIR2 for the respective directories. The "dirlist" is the list of sub-directores at this level of the hierarchy; the root contains DIR1 and DIR2, while each sub-directory has no sub-sub-directories and hence has an empty list. The "filelist" is the list of files at this level of the hierarchy; the root contains no files so has an empty list, while DIR1 contains FOO.;1 and BAR.;1 and DIR2 contains BAZ.;1.

for dirname, dirlist, filelist in iso.walk(iso_path='/DIR1'):
    print("Dirname:", dirname, ", Dirlist:", dirlist, ", Filelist:", filelist)

The second call to walk starts in the DIR1 subdirectory, so the output from this loop looks like:

Dirname: /DIR1 , Dirlist: [] , Filelist: ['FOO.;1', 'BAR.;1']

Like we saw before, the "dirname" for this level is /DIR1, while the "dirlist" is empty since there are no subdirectories, and the filelist contains FOO.;1 and BAR.;1.

iso.close()

Close out the ISO object to release resources and allow it to be reused.