Fastest way to convert a dict's keys & values from `unicode` to `str`?

DATA = { u'spam': u'eggs', u'foo': frozenset([u'Gah!']), u'bar': { u'baz': 97 },
         u'list': [u'list', (True, u'Maybe'), set([u'and', u'a', u'set', 1])]}

def convert(data):
    if isinstance(data, basestring):
        return str(data)
    elif isinstance(data, collections.Mapping):
        return dict(map(convert, data.iteritems()))
    elif isinstance(data, collections.Iterable):
        return type(data)(map(convert, data))
    else:
        return data

print DATA
print convert(DATA)
# Prints:
# {u'list': [u'list', (True, u'Maybe'), set([u'and', u'a', u'set', 1])], u'foo': frozenset([u'Gah!']), u'bar': {u'baz': 97}, u'spam': u'eggs'}
# {'bar': {'baz': 97}, 'foo': frozenset(['Gah!']), 'list': ['list', (True, 'Maybe'), set(['and', 'a', 'set', 1])], 'spam': 'eggs'}

Assumptions:

• You've imported the collections module and can make use of the abstract base classes it provides
• You're happy to convert using the default encoding (use data.encode('utf-8') rather than str(data) if you need an explicit encoding).

If you need to support other container types, hopefully it's obvious how to follow the pattern and add cases for them.

I know I'm late on this one:

def convert_keys_to_string(dictionary):
    """Recursively converts dictionary keys to strings."""
    if not isinstance(dictionary, dict):
        return dictionary
    return dict((str(k), convert_keys_to_string(v)) 
        for k, v in dictionary.items())

If you wanted to do this inline and didn't need recursive descent, this might work:

DATA = { u'spam': u'eggs', u'foo': True, u'bar': { u'baz': 97 } }
print DATA
# "{ u'spam': u'eggs', u'foo': True, u'bar': { u'baz': 97 } }"

STRING_DATA = dict([(str(k), v) for k, v in data.items()])
print STRING_DATA
# "{ 'spam': 'eggs', 'foo': True, 'bar': { u'baz': 97 } }"