PEP: 291
Title: Backward Compatibility for Standard Library
Version: $Revision$
Last-Modified: $Date$
Author: neal@metaslash.com (Neal Norwitz)
Status: Active
Type: Informational
Created: 06-Jun-2002
Post-History:
Python-Version: 2.3


Abstract

    This PEP describes the packages and modules in the standard
    library which should remain backward compatible with previous
    versions of Python.


Rationale

    Authors have various reasons why packages and modules should
    continue to work with previous versions of Python.  In order to
    maintain backward compatibility for these modules while moving the
    rest of the standard library forward, it is necessary to know
    which modules can be modified and which should use old and
    possibly deprecated features.

    Generally, authors should attempt to keep changes backward
    compatible with the previous released version of Python in order
    to make bug fixes easier to backport.

    In addition to a package or module being listed in this PEP, 
    authors must add a comment at the top of each file documenting
    the compatibility requirement.


Features to Avoid

    The following list contains common features to avoid in order
    to maintain backward compatibility with each version of Python.
    This list is not complete!  It is only meant as a general guide.

    Note that the features below were implemented in the version
    following the one listed.  For example, features listed next to
    1.5.2 were implemented in 2.0.

        Version    Features to Avoid
        -------    -----------------
          1.5.2    string methods, Unicode, list comprehensions, 
                   augmented assignment (eg, +=), zip(), import x as y,
                   dict.setdefault(), print >> f, calling f(*args, **kw),
                   plus all features below

          2.0      nested scopes, rich comparisons, function attributes,
                   plus all features below

          2.1      use of object or new-style classes, iterators, 
                   using generators, nested scopes, or //
                   without from __future__ import ... statement,
                   plus all features below

          2.2      bool, True, False, basestring, enumerate(), {}.pop(),
                   PendingDeprecationWarning, Universal Newlines


Backward Compatible Packages, Modules, and Tools

    Package/Module     Maintainer(s)          Python Version
    --------------     -------------          --------------
    bsddb              Barry Warsaw                2.1
    compiler           Jeremy Hylton               2.1
    distutils          Andrew Kuchling             1.5.2
    email              Barry Warsaw                2.1
    logging            Vinay Sajip                 1.5.2
    sre                Fredrik Lundh               1.5.2
    xml (PyXML)        Martin v. Loewis            2.0
    xmlrpclib          Fredrik Lundh               1.5.2


    Tool                         Maintainer(s)   Python Version
    ----                         -------------   --------------
    None


Copyright

    This document has been placed in the public domain.



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