Update a nested dictionary or similar mapping.

    Modify ``source`` in place.

    :type source: collections.Mapping
    :type overrides: collections.Mapping
    :rtype: collections.Mapping

def deep_update(source, overrides):
    """Update a nested dictionary or similar mapping.

    Modify ``source`` in place.

    :type source: collections.Mapping
    :type overrides: collections.Mapping
    :rtype: collections.Mapping
    """
    for key, value in overrides.items():
        if isinstance(value, collections.Mapping) and value:
            returned = deep_update(source.get(key, {}), value)
            source[key] = returned
        else:
            source[key] = overrides[key]
    return source