diff contrib/hgdiff @ 8527:f9a80054dd3c

use 'x is None' instead of 'x == None'

The built-in None object is a singleton and it is therefore safe to
compare memory addresses with is. It is also faster, how much depends
on the object being compared. For a simple type like str I get:

            | s = "foo" | s = None
  ----------+-----------+----------
  s == None | 0.25 usec | 0.21 usec
  s is None | 0.17 usec | 0.17 usec

--- a/contrib/hgdiff	Wed May 20 00:43:23 2009 +0200
+++ b/contrib/hgdiff	Wed May 20 00:52:46 2009 +0200
@@ -37,13 +37,13 @@
                 names[os.path.join(l, x)] = (st.st_dev, st.st_ino)
 
 def diff_files(file1, file2):
-    if file1 == None:
+    if file1 is None:
         b = file(file2).read().splitlines(1)
         l1 = "--- %s\n" % (file2)
         l2 = "+++ %s\n" % (file2)
         l3 = "@@ -0,0 +1,%d @@\n" % len(b)
         l = [l1, l2, l3] + ["+" + e for e in b]
-    elif file2 == None:
+    elif file2 is None:
         a = file(file1).read().splitlines(1)
         l1 = "--- %s\n" % (file1)
         l2 = "+++ %s\n" % (file1)