typed.py

from collections import namedtuple, OrderedDict
import functools

import pytest

def typednamedtuple(name, fields):
    factory = namedtuple(name, fields.keys())
    @functools.wraps(factory)
    def wrapper(*args, **kwargs):
        for spec, arg in zip(fields.iteritems(), args):
            if not isinstance(arg, spec[1]):
                raise TypeError(u'{} must be of type {}'.format(arg, spec[1]))
        for fieldname, value in kwargs.iteritems():
            if not isinstance(value, fields[fieldname]):
                raise TypeError(u'{} must be of type {}'.format(arg, fields[fieldname]))
        return factory(*args, **kwargs)


    return wrapper


#########################
# Example usage and tests

types = OrderedDict([
    ('key', basestring),
    ('value', object)
])
KeyValue = typednamedtuple('KeyValue', types)


def test_instantiation():
    kv = KeyValue(u'types', types)
    #assert isinstance(kv, KeyValue)
    assert kv.key == u'types'
    assert kv.value == types

def test_type_checking():
    with pytest.raises(TypeError):
        kv = KeyValue(43, types)

def test_named_args():
    kv = KeyValue(key=u'types', value=types)
    assert kv.key == u'types'
    assert kv.value == types
    assert kv[0] is kv.key
    assert kv[1] is kv.value