it's 2017; provide a sorting key function

README.md

@@ -120,11 +120,11 @@ Compare two arbitrary version strings
     >>> Dpkg.compare_versions(ver_1, ver_2)
     -1
 
-Use as a cmp function to sort a list of version strings
+Use as a key function to sort a list of version strings
 -------------------------------------------------------
 
     >>> from pydpkg import Dpkg
-    >>> sorted(['0:1.0-test1', '1:0.0-test0', '0:1.0-test2'] , cmp=Dpkg.compare_versions)
+    >>> sorted(['0:1.0-test1', '1:0.0-test0', '0:1.0-test2'] , key=Dpkg.compare_versions_key)
     ['0:1.0-test1', '0:1.0-test2', '1:0.0-test0']
 
 Use the `dpkg-inspect.py` script to inspect packages

pydpkg/__init__.py

@@ -13,6 +13,7 @@ import tarfile
 from gzip import GzipFile
 from hashlib import md5, sha1, sha256
 from email import message_from_string as Message
+from functools import cmp_to_key
 
 # pypi imports
 import six
@@ -520,3 +521,17 @@ class Dpkg(object):
         # at this point, the versions are equal, but due to an interpolated
         # zero in either the epoch or the debian version
         return 0
+
+    @staticmethod
+    def compare_versions_key(x):
+        """Uses functools.cmp_to_key to convert the compare_versions()
+        function to a function suitable to passing to sorted() and friends
+        as a key."""
+        return cmp_to_key(Dpkg.compare_versions)(x)
+
+    @staticmethod
+    def dstringcmp_key(x):
+        """Uses functools.cmp_to_key to convert the dstringcmp()
+        function to a function suitable to passing to sorted() and friends
+        as a key."""
+        return cmp_to_key(Dpkg.dstringcmp)(x)

setup.py

@@ -1,6 +1,6 @@
 from distutils.core import setup
 
-__VERSION__ = '1.2.0'
+__VERSION__ = '1.2.1'
 
 setup(
     name='pydpkg',

tests/test_dpkg.py

@@ -2,7 +2,6 @@
 
 import os
 import unittest
-from functools import cmp_to_key
 from email.message import Message
 
 from pydpkg import Dpkg, DpkgVersionError
@@ -100,7 +99,7 @@ class DpkgVersionsTest(unittest.TestCase):
         # http://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version
         self.assertEqual(
             sorted(['a', '', '~', '~~a', '~~'],
-                   key=cmp_to_key(Dpkg.dstringcmp)),
+                   key=Dpkg.dstringcmp_key),
             ['~~', '~~a', '~', '', 'a'])
 
     def test_compare_revision_strings(self):