python: Use key-functions when sorting containers

In Python 2, the traditional way to sort containers was to use a
comparison function (which returned either -1, 0 or 1 when passed two
objects) and pass that as the "cmp" argument to the container's sort()
method.

Python 2.4 introduced key-functions, which instead only operate on a
given item, and return a sorting key for this item.

In general, this runs faster, because the cmp-function has to get run
multiple times for each item of the container.

Python 3 removed the cmp-function, enforcing usage of key-functions
instead.

This change makes the script compatible with Python 2 and Python 3.

Signed-off-by: Mathieu Bridon <bochecha@daitauha.fr>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

src/mapi/mapi_abi.py

@@ -32,6 +32,7 @@ import os
 GLAPI = os.path.join(".", os.path.dirname(sys.argv[0]), "glapi/gen")
 sys.path.append(GLAPI)
 
+from operator import attrgetter
 import re
 from optparse import OptionParser
 import gl_XML
@@ -291,7 +292,7 @@ class ABIPrinter(object):
 
         # sort entries by their names
         self.entries_sorted_by_names = self.entries[:]
-        self.entries_sorted_by_names.sort(lambda x, y: cmp(x.name, y.name))
+        self.entries_sorted_by_names.sort(key=attrgetter('name'))
 
         self.indent = ' ' * 3
         self.noop_warn = 'noop_warn'
@@ -441,7 +442,7 @@ class ABIPrinter(object):
         """Return the string pool for use by stubs."""
         # sort entries by their names
         sorted_entries = self.entries[:]
-        sorted_entries.sort(lambda x, y: cmp(x.name, y.name))
+        sorted_entries.sort(key=attrgetter('name'))
 
         pool = []
         offsets = {}