[gnome-sudoku] Fix sort syntax error

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 93f53fb4eab1451b6b0b002611c539da5c0d76ab
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Thu Nov 7 22:17:26 2013 -0600

    Fix sort syntax error
    
    I don't dare try to determine what this lambda is trying to do, so let's
    use a sledgehammer to make it work. This requires a Python version bump,
    but we haven't released since the port to Python 3, so that's hardly a
    big deal.

 configure.ac      |    2 +-
 src/lib/sudoku.py |    6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 7de6ac9..a53891c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6,7 +6,7 @@ GNOME_MAINTAINER_MODE_DEFINES
 
 GLIB_GSETTINGS
 
-AM_PATH_PYTHON([3.0],,AC_MSG_ERROR([Python not found]))
+AM_PATH_PYTHON([3.2],,AC_MSG_ERROR([Python not found]))
 
 dnl ###########################################################################
 dnl Dependencies
diff --git a/src/lib/sudoku.py b/src/lib/sudoku.py
index 394c1d1..9170537 100644
--- a/src/lib/sudoku.py
+++ b/src/lib/sudoku.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+import functools
 import random
 import math
 import re
@@ -445,8 +446,9 @@ class SudokuSolver (SudokuGrid):
                 print('Solved!')
             return True
         # otherwise, find the possibility with the least possibilities
-        poss.sort(lambda a, b: len(a[1]) > len(b[1]) and 1 or len(a[1]) < len(b[1]) and -1 or \
-                  a[0] > b[0] and 1 or a[1] < b[1] and -1 or 0)
+        poss.sort(key=functools.cmp_to_key(lambda a, b: len(a[1]) > len(b[1]) \
+                                  and 1 or len(a[1]) < len(b[1]) and -1 or \
+                                  a[0] > b[0] and 1 or a[1] < b[1] and -1 or 0))
         least = poss[0]
         # remove anything we've already guessed
         possible_values = least[1] - self.guesses.guesses_for_coord(*least[0])