def flatten_mapping(mapping):
return {<EOL>key: value<EOL>for keys, value in mapping.items()<EOL>for key in always_iterable(keys)<EOL>}<EOL>
For every key that has an __iter__ method, assign the values
to a key for each.

>>> flatten_mapping({'ab': 3, ('c','d'): 4}) == {'ab': 3, 'c': 4, 'd': 4}
True