diff --git a/.travis.yml b/.travis.yml
index b84fe5a..a151ee5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,7 +18,7 @@ install:
   - pip install coveralls
 
 script:
-  - coverage run --source=src setup.py test
+  - coverage run --source=src --omit='src/mog_commons/backported/*' setup.py test
 
 after_success:
   - coveralls
diff --git a/src/mog_commons/__init__.py b/src/mog_commons/__init__.py
index e6d0c4f..377e1f6 100644
--- a/src/mog_commons/__init__.py
+++ b/src/mog_commons/__init__.py
@@ -1 +1 @@
-__version__ = '0.1.12'
+__version__ = '0.1.13'
diff --git a/src/mog_commons/backported/__init__.py b/src/mog_commons/backported/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/mog_commons/backported/inspect2.py b/src/mog_commons/backported/inspect2.py
new file mode 100644
index 0000000..c07df72
--- /dev/null
+++ b/src/mog_commons/backported/inspect2.py
@@ -0,0 +1,102 @@
+# backported from https://github.com/python/cpython/blob/2.7/Lib/inspect.py
+
+import sys
+from inspect import ismethod, getargspec
+
+
+def getcallargs(func, *positional, **named):
+    """Get the mapping of arguments to values.
+
+    A dict is returned, with keys the function argument names (including the
+    names of the * and ** arguments, if any), and values the respective bound
+    values from 'positional' and 'named'."""
+    args, varargs, varkw, defaults = getargspec(func)
+    f_name = func.__name__
+    arg2value = {}
+
+    # The following closures are basically because of tuple parameter unpacking.
+    assigned_tuple_params = []
+
+    def assign(arg, value):
+        if isinstance(arg, str):
+            arg2value[arg] = value
+        else:
+            assigned_tuple_params.append(arg)
+            value = iter(value)
+            for i, subarg in enumerate(arg):
+                try:
+                    subvalue = next(value)
+                except StopIteration:
+                    raise ValueError('need more than %d %s to unpack' %
+                                     (i, 'values' if i > 1 else 'value'))
+                assign(subarg, subvalue)
+            try:
+                next(value)
+            except StopIteration:
+                pass
+            else:
+                raise ValueError('too many values to unpack')
+
+    def is_assigned(arg):
+        if isinstance(arg, str):
+            return arg in arg2value
+        return arg in assigned_tuple_params
+
+    if ismethod(func) and func.im_self is not None:
+        # implicit 'self' (or 'cls' for classmethods) argument
+        positional = (func.im_self,) + positional
+    num_pos = len(positional)
+    num_total = num_pos + len(named)
+    num_args = len(args)
+    num_defaults = len(defaults) if defaults else 0
+    for arg, value in zip(args, positional):
+        assign(arg, value)
+    if varargs:
+        if num_pos > num_args:
+            assign(varargs, positional[-(num_pos - num_args):])
+        else:
+            assign(varargs, ())
+    elif 0 < num_args < num_pos:
+        raise TypeError('%s() takes %s %d %s (%d given)' % (
+            f_name, 'at most' if defaults else 'exactly', num_args,
+            'arguments' if num_args > 1 else 'argument', num_total))
+    elif num_args == 0 and num_total:
+        if varkw:
+            if num_pos:
+                # XXX: We should use num_pos, but Python also uses num_total:
+                raise TypeError('%s() takes exactly 0 arguments '
+                                '(%d given)' % (f_name, num_total))
+        else:
+            raise TypeError('%s() takes no arguments (%d given)' %
+                            (f_name, num_total))
+    for arg in args:
+        if isinstance(arg, str) and arg in named:
+            if is_assigned(arg):
+                raise TypeError("%s() got multiple values for keyword "
+                                "argument '%s'" % (f_name, arg))
+            else:
+                assign(arg, named.pop(arg))
+    if defaults:  # fill in any missing values with the defaults
+        for arg, value in zip(args[-num_defaults:], defaults):
+            if not is_assigned(arg):
+                assign(arg, value)
+    if varkw:
+        assign(varkw, named)
+    elif named:
+        unexpected = next(iter(named))
+        try:
+            unicode
+        except NameError:
+            pass
+        else:
+            if isinstance(unexpected, unicode):
+                unexpected = unexpected.encode(sys.getdefaultencoding(), 'replace')
+        raise TypeError("%s() got an unexpected keyword argument '%s'" %
+                        (f_name, unexpected))
+    unassigned = num_args - len([arg for arg in args if is_assigned(arg)])
+    if unassigned:
+        num_required = num_args - num_defaults
+        raise TypeError('%s() takes %s %d %s (%d given)' % (
+            f_name, 'at least' if defaults else 'exactly', num_required,
+            'arguments' if num_required > 1 else 'argument', num_total))
+    return arg2value
diff --git a/src/mog_commons/types.py b/src/mog_commons/types.py
new file mode 100644
index 0000000..50840eb
--- /dev/null
+++ b/src/mog_commons/types.py
@@ -0,0 +1,158 @@
+from __future__ import division, print_function, absolute_import, unicode_literals
+
+import sys
+import six
+from abc import ABCMeta, abstractmethod
+
+if sys.version_info < (2, 7):
+    from mog_commons.backported.inspect2 import getcallargs
+else:
+    from inspect import getcallargs
+
+__all__ = [
+    'String',
+    'Unicode',
+    'ListOf',
+    'TupleOf',
+    'SetOf',
+    'DictOf',
+    'VarArg',
+    'KwArg',
+    'types',
+]
+
+#
+# Type definitions
+#
+String = six.string_types + (bytes,)
+
+Unicode = unicode if six.PY2 else str
+
+
+@six.add_metaclass(ABCMeta)
+class ComposableType(object):
+    """Label for composable types"""
+
+    @abstractmethod
+    def name(self):
+        """abstract method"""
+
+    @abstractmethod
+    def check(self, obj):
+        """abstract method"""
+
+
+@six.add_metaclass(ABCMeta)
+class IterableOf(ComposableType):
+    def __init__(self, iterable_type, elem_type):
+        self.iterable_type = iterable_type
+        self.elem_type = elem_type
+
+    def name(self):
+        return '%s(%s)' % (self.iterable_type.__name__, _get_name(self.elem_type))
+
+    def check(self, obj):
+        return isinstance(obj, self.iterable_type) and all(_check_type(elem, self.elem_type) for elem in obj)
+
+
+class ListOf(IterableOf):
+    """Label for list element type assertion"""
+
+    def __init__(self, elem_type):
+        IterableOf.__init__(self, list, elem_type)
+
+
+class TupleOf(IterableOf):
+    """Label for tuple element type assertion"""
+
+    def __init__(self, elem_type):
+        IterableOf.__init__(self, tuple, elem_type)
+
+
+class SetOf(IterableOf):
+    """Label for set element type assertion"""
+
+    def __init__(self, elem_type):
+        IterableOf.__init__(self, set, elem_type)
+
+
+class DictOf(ComposableType):
+    """Label for dict element type assertion"""
+
+    def __init__(self, key_type, value_type):
+        self.key_type = key_type
+        self.value_type = value_type
+
+    def name(self):
+        return 'dict(%s->%s)' % (_get_name(self.key_type), _get_name(self.value_type))
+
+    def check(self, obj):
+        return isinstance(obj, dict) and all(
+            _check_type(k, self.key_type) and _check_type(v, self.value_type) for k, v in obj.items())
+
+
+def VarArg(cls):
+    """Shorthand description for var arg"""
+    return TupleOf(cls)
+
+
+def KwArg(cls):
+    """Shorthand description for keyword arg"""
+    return DictOf(String, cls)
+
+
+#
+# Helper functions
+#
+def _get_name(cls):
+    if isinstance(cls, ComposableType):
+        return cls.name()
+    if isinstance(cls, tuple):
+        return '(%s)' % '|'.join(_get_name(t) for t in cls)
+    else:
+        return cls.__name__
+
+
+def _check_type(obj, cls):
+    return cls.check(obj) if isinstance(cls, ComposableType) else isinstance(obj, cls)
+
+
+#
+# Decorators
+#
+def types(*return_type, **arg_types):
+    """
+    Assert types of the function arguments and return value.
+    :param return_type: expected type of the return value
+    :param arg_types: expected types of the arguments
+
+    :example:
+    @types(float, x=int, y=float, z=ListOf(int))
+    def f(x, y, z):
+        return x * y + sum(z)
+    """
+    assert len(return_type) <= 1, 'You can specify at most one return type.'
+
+    arg_msg = '%s must be %s, not %s.'
+    return_msg = 'must return %s, not %s.'
+
+    def f(func):
+        import functools
+
+        @functools.wraps(func)
+        def wrapper(*args, **kwargs):
+            # convert args to call args
+            call_args = getcallargs(func, *args, **kwargs)
+
+            for arg_name, expect in arg_types.items():
+                assert arg_name in call_args, 'Not found argument: %s' % arg_name
+                actual = call_args[arg_name]
+                assert _check_type(actual, expect), arg_msg % (arg_name, _get_name(expect), type(actual).__name__)
+
+            ret = func(*args, **kwargs)
+            if return_type:
+                assert _check_type(ret, return_type[0]), return_msg % (_get_name(return_type[0]), type(ret).__name__)
+            return ret
+        return wrapper
+
+    return f
diff --git a/tests/mog_commons/test_types.py b/tests/mog_commons/test_types.py
new file mode 100644
index 0000000..67140f3
--- /dev/null
+++ b/tests/mog_commons/test_types.py
@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -*-
+from __future__ import division, print_function, absolute_import, unicode_literals
+
+import six
+from mog_commons import unittest
+from mog_commons.types import *
+from mog_commons.types import _get_name
+
+
+class TestTypes(unittest.TestCase):
+    @staticmethod
+    @types(int, x=int, y=int)
+    def bin_func(x, y):
+        return x + y
+
+    @staticmethod
+    @types(p1=int, p2=ListOf(int), p3=int, p4=String, p5=String, k=VarArg(ListOf(DictOf(String, SetOf(int)))),
+           kw=KwArg(float))
+    def complex_func(p1, p2, p3, p4='xxx', p5='yyy', *k, **kw):
+        return 1
+
+    @staticmethod
+    @types(a=str)
+    def err_func1(b):
+        return b
+
+    @staticmethod
+    def err_func2():
+        @types(bool, int)
+        def f():
+            pass
+        return 1
+
+    @staticmethod
+    @types(bool)
+    def predicate():
+        return 1
+
+    def test_types(self):
+        str_type = '(basestring|str)' if six.PY2 else '(str|bytes)'
+
+        self.assertEqual(self.bin_func(10, 20), 30)
+        self.assertRaisesMessage(AssertionError, 'x must be int, not dict.', self.bin_func, {}, 20)
+        self.assertRaisesMessage(AssertionError, 'y must be int, not list.', self.bin_func, 10, [])
+
+        self.assertEqual(self.complex_func(123, [1, 2], 10, 'abc', 'def', [{'x': set([3, 4, 5])}]), 1)
+        self.assertRaisesMessage(AssertionError, 'kw must be dict(%s->float), not dict.' % str_type,
+                                 self.complex_func, 123, [1, 2], 10, 'abc', 'def', [{'x': set([3, 4, 5])}], x='12.3')
+
+        self.assertRaisesMessage(AssertionError, 'must return bool, not int.', self.predicate)
+
+    def test_types_error(self):
+        self.assertRaisesMessage(AssertionError, 'Not found argument: a', self.err_func1, 123)
+        self.assertRaisesMessage(AssertionError, 'You can specify at most one return type.', self.err_func2)
+
+    def test_get_name(self):
+        str_type = '(basestring|str)' if six.PY2 else '(str|bytes)'
+        unicode_type = 'unicode' if six.PY2 else 'str'
+
+        self.assertEqual(_get_name(int), 'int')
+        self.assertEqual(_get_name(String), str_type)
+        self.assertEqual(_get_name(Unicode), unicode_type)
+        self.assertEqual(_get_name(TupleOf(int)), 'tuple(int)')
+        self.assertEqual(_get_name(ListOf(int)), 'list(int)')
+        self.assertEqual(_get_name(SetOf(int)), 'set(int)')
+        self.assertEqual(_get_name(DictOf(int, float)), 'dict(int->float)')
+        self.assertEqual(_get_name(VarArg(str)), 'tuple(str)')
+        self.assertEqual(_get_name(KwArg(str)), 'dict(%s->str)' % str_type)
+        self.assertEqual(_get_name(KwArg(ListOf(DictOf(float, SetOf((str, TupleOf(Unicode))))))),
+                         'dict(%s->list(dict(float->set((str|tuple(%s))))))' % (str_type, unicode_type))