Update Readme.md

chaniel · web-flow · commit 35653c561489 · 2016-10-02T12:43:07.000+08:00
diff --git a/Readme.md b/Readme.md
@@ -669,6 +669,9 @@ Note that the syntax changed in Python 3.0: you can just say super().__init__()
 http://stackoverflow.com/questions/576169/understanding-python-super-with-init-methods
 
 ## 30 range and xrange
+都在循环时使用，xrange内存性能更好。
+for i in range(0, 20):
+for i in xrange(0, 20):
 What is the difference between range and xrange functions in Python 2.X?
  range creates a list, so if you do range(1, 10000000) it creates a list in memory with 9999999 elements.
  xrange is a sequence object that evaluates lazily.
