Import ABCs from collections.abc. Fixes #27.

ensure/_types.py

@@ -12,6 +12,7 @@
 class NumericStringType(type):
     _type = str
     _cast = float
+
     def __instancecheck__(self, other):
         try:
             if not isinstance(other, self._type):

ensure/main.py

@@ -1,12 +1,11 @@
 from __future__ import absolute_import, division, print_function, unicode_literals
 
 import sys
-import collections
 import types
 import re
-import functools
 from unittest.case import TestCase
-from collections import namedtuple, Mapping, Iterable
+from collections.abc import Mapping, Iterable
+
 from six import string_types
 
 from ._types import NumericString, NumericByteString, IntegerString, IntegerByteString

setup.cfg

@@ -2,4 +2,4 @@
 universal=1
 [flake8]
 max-line-length=120
-ignore: E301, E302, E401, E226, F841, F401
+ignore: E302, E401, F401