python中while循环的停止点

Question

i=0
>>> while i<3:
...     print i
...     i += 1
... else:
...     print ‘Done with i =’, i
...
0
1
2
Done with i = 3

Hi all, I am wondering why the while loop is done when i=3, not when i=2. When i=2, i=i+1=2+1=3, the expression becomes False, then execution gets finished. Isn't that right?

Answer 1

The else in a while ... else block always executes. So your while loop ends with i == 2 , but then you increment with i += 1 , so i == 3 . Then your while loop quits, and you perform the else block.

Answer 2

That else block will always execute. It's the same as simply writing print "Done with i =", i . As BlivetWidget said, you are adding 1 to i and then executing the else block. Instead, you could use print "Done with i = ", i-1 .