Calculate difference in keys contained in two Python dictionaries

Question

Suppose I have two Python dictionaries - dictA and dictB. I need to find out if there are any keys which are present in dictB but not

Answer 1

As mentioned in other answers, unittest produces some nice output for comparing dicts, but in this example we don't want to have to build a whole test first.

Scraping the unittest source, it looks like you can get a fair solution with just this:

import difflib
import pprint

def diff_dicts(a, b):
    if a == b:
        return ''
    return '\n'.join(
        difflib.ndiff(pprint.pformat(a, width=30).splitlines(),
                      pprint.pformat(b, width=30).splitlines())
    )

so

dictA = dict(zip(range(7), map(ord, 'python')))
dictB = {0: 112, 1: 'spam', 2: [1,2,3], 3: 104, 4: 111}
print diff_dicts(dictA, dictB)

Results in:

{0: 112,
-  1: 121,
-  2: 116,
+  1: 'spam',
+  2: [1, 2, 3],
   3: 104,
-  4: 111,
?        ^

+  4: 111}
?        ^

-  5: 110}

Where:

• '-' indicates key/values in the first but not second dict
• '+' indicates key/values in the second but not the first dict

Like in unittest, the only caveat is that the final mapping can be thought to be a diff, due to the trailing comma/bracket.