# Source code for flyforms.common

    # coding=utf-8
    from collections import Iterable, Mapping

    from flyforms.compatibility import string_types

    UNSET = object()  # the default mark for not set values

    is_set = lambda value: value is not UNSET

    # Supported types for JSON encoding and decoding operations
    jsonify_types = (bool, int, float, Iterable, Mapping) + string_types

    class FrozenDict(Mapping):
        """
        Immutable dictionary implementation
        stolen from StackOverflow_

        .. _StackOverflow: http://stackoverflow.com/questions/2703599/what-would-a-frozen-dict-be
        """

        def __init__(self, *args, **kwargs):
            self._d = dict(*args, **kwargs)
            self._hash = None

        def __iter__(self):
            return iter(self._d)

        def __len__(self):
            return len(self._d)

        def __getitem__(self, key):
            return self._d[key]

        def __hash__(self):
            if self._hash is None:
                self._hash = 0
                for pair in self.iteritems():
                    self._hash ^= hash(pair)
            return self._hash