README.deb822

deb822.py README
================

The Python deb822 aims to provide a dict-like interface to various rfc822-like
Debian data formats, like Packages/Sources, .changes/.dsc, pdiff Index files,
etc. The benefit is that deb822 knows about special fields that contain
whitespace separated sub-fields, and provides named access to them. For
example, the "Files" field in Source packages, which has three subfields, or
"Files" in .changes files, which has five. These are known as "multifields".

deb822 has no external dependencies, but can use python-apt if available to
parse the data, which gives a very significant performance boost when iterating
over big Packages files.

Key lookup in Deb822 objects and their multifields is case-insensitive, but the
original case is always preserved, e.g. when printing the object.


Classes
=======

Here is a list of the types deb822 knows about:

  * Deb822 (aliases: Packages) - base class with no multifields.

  * Dsc (aliases: Sources) - class to represent .dsc files / Sources paragraphs.

    - Multivalued fields:

      · Files: md5sum, size, name

  * Changes - class to represent a .changes file

    - Multivalued fields:

      · Files: md5sum, size, section, priority, name

  * PdiffIndex - class to represent a pdiff Index file

    - Multivalued fields:

      · SHA1-Current: SHA1, size
      · SHA1-History: SHA1, size, date
      · SHA1-Patches: SHA1, size, date


Input
=====

Deb822 objects are normally initialized from a file() object, from which
at most one paragraph is read, or a string.

Alternatively, any sequence that returns one line of input at a time may
be used, e.g. an array of strings.

PGP signatures, if present, will be stripped.


Iteration
=========

All classes provide an "iter_paragraphs" class method to easily go over
each stanza in a file with multiple entries, like a Packages.gz file.
For example:

    f = file('/mirror/debian/dists/sid/main/binary-i386/Sources') 

    for src in Sources.iter_paragraphs(f):
	print src['Package'], src['Version']

This method uses python-apt if available to parse the file, since it
significantly boosts performance. The downside, though, is that yielded
objects share storage, so they should never be kept accross iterations.
To prevent this behavior, pass a "shared_storage=False" keyword-argument
to the iter_paragraphs() function.


Sample usage (TODO: Improve)
============

   import deb822 

   d = deb822.dsc(file('foo_1.1.dsc'))
   source = d['Source']
   version = d['Version']

   for f in d['Files']:
       print 'Name:', f['name']
       print 'Size:', f['size']
       print 'MD5sum:', f['md5sum']

    # If we like, we can change fields
    d['Standards-Version'] = '3.7.2'

    # And then dump the new contents
    new_dsc = open('foo_1.1.dsc2', 'w')
    d.dump(new_dsc)
    new_dsc.close()