Automatic Argument Conversion Decorator

arg_types.py

import calendar
from datetime import datetime
import types
import json
from functools import wraps

def convert_arg(type_name, value):
    converter = None
    if not isinstance(type_name, basestring):
        converter = type_name
        type_name = type_name.__name__

    if isinstance(value, basestring):
        if type_name == 'list':
            try:
                value = json_decode(value)
            except ValueError:
                value = [value]
        elif type_name == 'tuple':
            value = (value,)
        elif type_name == 'datetime':
            try:
                value = float(value)
            except ValueError:
                value = None
            else:
                value = datetime.fromtimestamp(value)
        elif type_name == 'dict':
            value = json.loads(value)
        elif type_name == 'int':
            value = int(value)
        elif type_name == 'long':
            value = long(value)
        elif type_name == 'float':
            value = float(value)
        elif type_name == 'bool':
            value = (value.lower() == 'true') or (value.lower() == 'yes') or (value.lower() == '1')
        elif converter is not None:
            value = converter(value)
    elif isinstance(value, int) or isinstance(value, float):
        if type_name == 'datetime':
            value = datetime.fromtimestamp(float(value))

    if value is not None and type(value).__name__ != type_name and not converter:
        raise TypeError("Expecting <type '" + type_name + "'>")

    return value


def arg_types(**params):
    def _decorator(func):
        if isinstance(func, staticmethod):
            func = func.__func__

        @wraps(func)
        def _inner(*args, **kwargs):
            argSpec = getargspec(func)
            argNames = argSpec.args

            numArgs = len(args)

            newArgs = []

            i = 0
            for argName in argNames:

                if i < numArgs:
                    value = args[i]
                    i += 1
                else:
                    value = kwargs[argName]

                if argName in params:
                    try:
                        value = convert_arg(params[argName], value)
                    except TypeError as err:
                        raise TypeError(func.__name__ + ": Argument '" + argName + "' given incorrect type. " + str(err))
                    except ValueError as err:
                        raise ValueError(func.__name__ + ": Cannot convert " + str(type(value).__name__) + " argument '" + argName + "' to " + str(params[argName]) + '. ' + str(err))

                newArgs.append(value)

            return func(*newArgs)

        return _inner
    return _decorator


def test_arg_types():

    class Dummy(object):
        def __init__(self, arg):
            self.arg = arg

        def __str__(self):
            return self.arg

    @arg_types(date=datetime, number=int, isAwesome=bool, dummy=Dummy, things='list', stuff=dict)
    def testfunc(date, number, isAwesome, dummy=None, things=[], stuff={}):
        assert type(date) == datetime
        assert str(date) == '2014-09-08 15:46:49+00:00'

        assert type(number) == int
        assert number == 42

        assert type(isAwesome) == bool and isAwesome

        assert isinstance(dummy, Dummy) and str(dummy) == 'test'

        assert things[0] == 'a thing'
        assert stuff['foo'] == 'bar'

    testfunc('1410191209', '42', 'true', 'test', stuff='{"foo": "bar"}', things='a thing')
    testfunc(1410191209, 42, 'yes', 'test', stuff={"foo": "bar"}, things='["a thing", "of Things"]')

    print 'All Tests Passed'