diff --git a/dice/roller.py b/dice/roller.py
index 58a7f21..a03c722 100644
--- a/dice/roller.py
+++ b/dice/roller.py
@@ -70,7 +70,7 @@ class DiceRoller(object):
 
         output = ""
         repeat = 1
-        if trials != None:
+        if trials is not None:
             repeat = trials
         for i in range(repeat):
             mode = 1
@@ -86,8 +86,8 @@ class DiceRoller(object):
                 # m[0] = (keep, num dice)
                 # m[1] = num faces on the die
                 if type(m) == tuple:
-                    if m[0] != None:
-                        if m[0][0] != None:
+                    if m[0] is not None:
+                        if m[0][0] is not None:
                             keep = m[0][0]
                         dice = m[0][1]
                     size = m[1]
@@ -113,14 +113,14 @@ class DiceRoller(object):
                     curr_str += str(m)
                 total += mode * res
             if repeat == 1:
-                if comment != None:
+                if comment is not None:
                     output = "%d %s (%s)" % (total, comment.strip(), curr_str)
                 else:
                     output = "%d (%s)" % (total, curr_str)
             else:
                 output += "%d (%s)" % (total, curr_str)
                 if i == repeat - 1:
-                    if comment != None:
+                    if comment is not None:
                         output += " (%s)" % (comment.strip())
         return output