args / kwargs hash - works in python 2 & 3. Useful for memoizers.

args_hash.py

def _tob(_string, enc='utf8'):
    if isinstance(_string, unicode):
        return _string.encode(enc)
    return b'' if _string is None else bytes(_string)


def args_hash(*args, **kw):
    """Calculate a hash value from string args and kwargs.

    Given the same positional arguments and keyword
    arguments, this function will produce the same
    hash key.
    """
    items = list(args) + [i for t in sorted(kw.items()) for i in t]
    items = ('__NoneType__' if _i is None else _i
             for _i in items)
    # All items must be strings
    args_string = '|'.join(items)
    return hashlib.sha1(_tob(args_string)).hexdigest()

test_args_hash.py

from args_hash import args_hash

class TestArgsHash:

    def test_kw_order_agnostic(self):
        h1 = args_hash(
            'one', 'two', 'three', four='4', five='five')
        h2 = args_hash(
            'one', 'two', 'three', five='five', four='4')
        assert h1
        assert h2
        assert h1 == h2

    def test_empty_case(self):
        h1 = args_hash()
        h2 = args_hash()
        assert h1
        assert h2
        assert h1 == h2

    def test_null_case(self):
        h1 = args_hash(None)
        h2 = args_hash(None)
        assert h1
        assert h2
        assert h1 == h2

    def test_null_case_kw(self):
        kw = {'': None}
        h1 = args_hash(None, **kw)
        h2 = args_hash(None, **kw)
        assert h1
        assert h2
        assert h1 == h2

    def test_cannot_hash_non_string_int(self):
        with pytest.raises(TypeError) as excinfo:
            args_hash(1)
        assert excinfo.type == TypeError
        assert 'int found' in str(excinfo.value)

    def test_cannot_hash_non_string_list(self):
        with pytest.raises(TypeError) as excinfo:
            args_hash([1])
        assert excinfo.type == TypeError
        assert 'list found' in str(excinfo.value)

    def test_cannot_hash_non_string_dict(self):
        with pytest.raises(TypeError) as excinfo:
            args_hash({'hello': 'world'})
        assert excinfo.type == TypeError
        assert 'dict found' in str(excinfo.value)