Print diff of Python dictionaries

Question

I want to take two dictionaries and print a diff of them. This diff should include the differences in keys AND values. I've created this little snippet to achieve the results using built-in code in the unittest module. However, it's a nasty hack since I have to subclass unittest.TestCase and provide a runtest() method for it to work. In addition, this code will cause the application to error out since it will raise an AssertError when there are differences. All I really want is to print the diff.

import unittest
class tmp(unittest.TestCase):
    def __init__(self):
         # Show full diff of objects (dicts could be HUGE and output truncated)
        self.maxDiff = None
    def runTest():
        pass
_ = tmp()
_.assertDictEqual(d1, d2)

I was hoping to use the difflib module, but it looks to only work for strings. Is there some way to work around this and still use difflib?

Answer 1

Adapted from the cpython source:

https://github.com/python/cpython/blob/01fd68752e2d2d0a5f90ae8944ca35df0a5ddeaa/Lib/unittest/case.py#L1091

import difflib
import pprint

def compare_dicts(d1, d2):
    return ('\n' + '\n'.join(difflib.ndiff(
                   pprint.pformat(d1).splitlines(),
                   pprint.pformat(d2).splitlines())))