db/message: replace __cmp__ with rich comparisons

This replaces the deprecated __cmp__ function with the more modern
__lt__, __eq__, and __ne__, and then uses functools.total_ordering to
implemented the remaining pieces of the rich comparison protocol
automatically. It also make use of the NotImplemented singleton, which
python uses to signal to rich comparators that this class doesn't no how
to compare to the other class, which results in the complementary method
from the other class being used, and if both return NotImplemented than
a TypeError is generated.

There are two reasons to make this change. First, python 3 only supports
rich comparisons, and second rich comparisons are much faster than using
cmp (and the __cmp__ protocol) because cmp is called at least 3 times
per element, while a rich comparitor is called one per element.

functools.total_ordering is in the standard library from 2.7 and 3.3,
and will implement the rich comparison protocol provided that __eq__ and
at least one of __lt__, __le__, __ge__, or __gt__ are implemented. It
does not (oddly enough) implement __ne__, so I've implemented that
manually.

1 files changed, 16 insertions, 4 deletions

diff --git a/alot/db/message.py b/alot/db/message.py
index 5566fa64..2f5e61e3 100644
--- a/alot/db/message.py
+++ b/alot/db/message.py
@@ -3,6 +3,7 @@
 # For further details see the COPYING file
 import email
 import email.charset as charset
+import functools
 from datetime import datetime
 
 from notmuch import NullPointerError
@@ -16,6 +17,7 @@ from ..settings import settings
 charset.add_charset('utf-8', charset.QP, charset.QP, 'utf-8')
 
 
+@functools.total_ordering
 class Message(object):
 
     """
@@ -60,10 +62,20 @@ class Message(object):
         """needed for sets of Messages"""
         return hash(self._id)
 
-    def __cmp__(self, other):
-        """needed for Message comparison"""
-        res = cmp(self.get_message_id(), other.get_message_id())
-        return res
+    def __eq__(self, other):
+        if isinstance(other, type(self)):
+            return self.get_message_id() == other.get_message_id()
+        return NotImplemented
+
+    def __ne__(self, other):
+        if isinstance(other, type(self)):
+            return self.get_message_id() != other.get_message_id()
+        return NotImplemented
+
+    def __lt__(self, other):
+        if isinstance(other, type(self)):
+            return self.get_message_id() < other.get_message_id()
+        return NotImplemented
 
     def get_email(self):
         """returns :class:`email.Message` for this message"""