Django's legacy DotExpendedDict

dotexpandeddict.py

class DotExpandedDict(dict):
    """
    A special dictionary constructor that takes a dictionary in which the keys
    may contain dots to specify inner dictionaries. It's confusing, but this
    example should make sense.

    >>> d = DotExpandedDict({'person.1.firstname': ['Simon'], \
            'person.1.lastname': ['Willison'], \
            'person.2.firstname': ['Adrian'], \
            'person.2.lastname': ['Holovaty']})
    >>> d
    {'person': {'1': {'lastname': ['Willison'], 'firstname': ['Simon']}, '2': {'lastname': ['Holovaty'], 'firstname': ['Adrian']}}}
    >>> d['person']
    {'1': {'lastname': ['Willison'], 'firstname': ['Simon']}, '2': {'lastname': ['Holovaty'], 'firstname': ['Adrian']}}
    >>> d['person']['1']
    {'lastname': ['Willison'], 'firstname': ['Simon']}

    # Gotcha: Results are unpredictable if the dots are "uneven":
    >>> DotExpandedDict({'c.1': 2, 'c.2': 3, 'c': 1})
    {'c': 1}
    """
    def __init__(self, key_to_list_mapping):
        for k, v in key_to_list_mapping.items():
            current = self
            bits = k.split('.')
            for bit in bits[:-1]:
                current = current.setdefault(bit, {})
            # Now assign value to current position
            try:
                current[bits[-1]] = v
            except TypeError: # Special-case if current isn't a dict.
                current = {bits[-1]: v}