Python class to take the difference of two python dictionaries:

• what was added,
• what was removed,
• which key-value pairs are the same, and
• which key-value pairs are changed

Generates only top-level differences and does not recurse.

Originally presented in a [StackoverFlow answer] (http://stackoverflow.com/questions/1165352/fast-comparison-between-two-python-dictionary/1165552#1165552).