dulwich/dulwich/misc.py

# misc.py -- For dealing with python2.4 oddness
# Copyright (C) 2008 Canonical Ltd.
# 
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; version 2
# of the License or (at your option) a later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA  02110-1301, USA.
'''Misc utilities to work with python2.4.

These utilities can all be deleted when dulwich decides it wants to stop
support for python 2.4.
'''
try:
    import hashlib
except ImportError:
    import sha
import struct


class defaultdict(dict):
    '''A python 2.4 equivalent of collections.defaultdict.'''

    def __init__(self, default_factory=None, *a, **kw):
        if (default_factory is not None and
            not hasattr(default_factory, '__call__')):
            raise TypeError('first argument must be callable')
        dict.__init__(self, *a, **kw)
        self.default_factory = default_factory

    def __getitem__(self, key):
        try:
            return dict.__getitem__(self, key)
        except KeyError:
            return self.__missing__(key)

    def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        self[key] = value = self.default_factory()
        return value

    def __reduce__(self):
        if self.default_factory is None:
            args = tuple()
        else:
            args = self.default_factory,
        return type(self), args, None, None, self.items()

    def copy(self):
        return self.__copy__()

    def __copy__(self):
        return type(self)(self.default_factory, self)

    def __deepcopy__(self, memo):
        import copy
        return type(self)(self.default_factory,
                          copy.deepcopy(self.items()))
    def __repr__(self):
        return 'defaultdict(%s, %s)' % (self.default_factory,
                                        dict.__repr__(self))


def make_sha(source=''):
    '''A python2.4 workaround for the sha/hashlib module fiasco.'''
    try:
        return hashlib.sha1(source)
    except NameError:
        sha1 = sha.sha(source)
        return sha1


def unpack_from(fmt, buf, offset=0):
    '''A python2.4 workaround for struct missing unpack_from.'''
    try:
        return struct.unpack_from(fmt, buf, offset)
    except AttributeError:
        b = buf[offset:offset+struct.calcsize(fmt)]
        return struct.unpack(fmt, b)