def resolve_freezer(freezer):
    """
    Locate the appropriate freezer given FREEZER or string input from the programmer.

    :param freezer: FREEZER constant or string for the freezer that is requested.  (None = FREEZER.DEFAULT)
    :return:
    """
    # Set default freezer if there was none
    if not freezer:
        return _Default()

    # Allow character based lookups as well
    if isinstance(freezer, six.string_types):
        cls = _freezer_lookup(freezer)
        return cls()

    # Allow plain class definition lookups (we instantiate the class)
    if freezer.__class__ == type.__class__:
        return freezer()

    # Warn when a custom freezer implementation is used.
    if freezer not in FREEZER.ALL:
        warn(u"Using custom freezer implelmentation: {0}".format(freezer))

    return freezer
Locate the appropriate freezer given FREEZER or string input from the programmer.

    :param freezer: FREEZER constant or string for the freezer that is requested.  (None = FREEZER.DEFAULT)
    :return: