# dicthelpers.py - helper routines for Python dicts
#
# Copyright 2013 Facebook
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

def _diffjoin(d1, d2, default, compare):
    res = {}
    if d1 is d2 and compare:
        # same dict, so diff is empty
        return res

    for k1, v1 in d1.iteritems():
        if k1 in d2:
            v2 = d2[k1]
            if not compare or v1 != v2:
                res[k1] = (v1, v2)
        else:
            res[k1] = (v1, default)

    if d1 is d2:
        return res

    for k2 in d2:
        if k2 not in d1:
            res[k2] = (default, d2[k2])

    return res

def diff(d1, d2, default=None):
    return _diffjoin(d1, d2, default, True)

def join(d1, d2, default=None):
    return _diffjoin(d1, d2, default, False)