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
% init
% commit
adding base
% qnew mqbase
% qrefresh
% qdiff
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@
-base
+patched
% qdiff dirname
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@
-base
+patched
% qdiff filename
diff -r 67e992f2c4f3 base
--- a/base
+++ b/base
@@ -1,1 +1,1 @@
-base
+patched
% revert
% qpop
patch queue now empty
% qdelete mqbase
% commit 2
adding lines
% qnew 2
% qdiff -U 1
diff -r 35fb829491c1 lines
--- a/lines
+++ b/lines
@@ -1,1 +1,3 @@
+
+
1
@@ -4,4 +6,4 @@
4
-hello world
-goodbye world
+hello world
+ goodbye world
7
% qdiff -b
diff -r 35fb829491c1 lines
--- a/lines
+++ b/lines
@@ -1,9 +1,11 @@
+
+
1
2
3
4
-hello world
-goodbye world
+hello world
+ goodbye world
7
8
9
% qdiff -U 1 -B
diff -r 35fb829491c1 lines
--- a/lines
+++ b/lines
@@ -4,4 +6,4 @@
4
-hello world
-goodbye world
+hello world
+ goodbye world
7
qdiff -w
diff -r 35fb829491c1 lines
--- a/lines
+++ b/lines
@@ -1,3 +1,5 @@
+
+
1
2
3