For when an assertion comparing two massive dicts fails in a python unit test

nose_dictdiff.py

import sys
import datetime

# expect either a single line >> assert {.... dicta ....} == {.... dictb ....}
#  (as produced from nosetests -d assertion failures)
# or two dicts, on two separate lines.
# obviously the former breaks if == appears in a key or value...

line = sys.stdin.readline()

line, split, values = line.partition(">>  assert")

if len(split):
    a, b = values.split("==")
else:
    a, b = line, sys.stdin.readline()

a = eval(a)
b = eval(b)

class Undefined(object):
    def __str__(self):
        return "<undefined>"

for key in set(a) | set(b):
    ag = a.get(key, Undefined())
    bg = b.get(key, Undefined())
    if ag != bg:
        print key, ag, bg