在Python中模拟do-while循环? [英] Emulate a do-while loop in Python?
问题描述
我需要在Python程序中模拟do-while循环。不幸的是,以下简单代码无法正常工作:
I need to emulate a do-while loop in a Python program. Unfortunately, the following straightforward code does not work:
list_of_ints = [ 1, 2, 3 ]
iterator = list_of_ints.__iter__()
element = None
while True:
if element:
print element
try:
element = iterator.next()
except StopIteration:
break
print "done"
代替 1,2,3,done,它输出以下输出:
Instead of "1,2,3,done", it prints the following output:
[stdout:]1
[stdout:]2
[stdout:]3
None['Traceback (most recent call last):
', ' File "test_python.py", line 8, in <module>
s = i.next()
', 'StopIteration
']
为了捕获停止迭代异常并适当地中断
循环,我该怎么办?
What can I do in order to catch the 'stop iteration' exception and break a while loop properly?
为什么会出现这种情况的示例
An example of why such a thing may be needed is shown below as pseudocode.
状态机:
s = ""
while True :
if state is STATE_CODE :
if "//" in s :
tokens.add( TOKEN_COMMENT, s.split( "//" )[1] )
state = STATE_COMMENT
else :
tokens.add( TOKEN_CODE, s )
if state is STATE_COMMENT :
if "//" in s :
tokens.append( TOKEN_COMMENT, s.split( "//" )[1] )
else
state = STATE_CODE
# Re-evaluate same line
continue
try :
s = i.next()
except StopIteration :
break
推荐答案
我不确定您要做什么。您可以像这样实现一个do-while循环:
I am not sure what you are trying to do. You can implement a do-while loop like this:
while True:
stuff()
if fail_condition:
break
或:
stuff()
while not fail_condition:
stuff()
您正在尝试使用do while循环来打印列表中的内容吗?为什么不只使用:
What are you doing trying to use a do while loop to print the stuff in the list? Why not just use:
for i in l:
print i
print "done"
更新:
所以您有列表线?而您想继续迭代呢?怎么样:
So do you have a list of lines? And you want to keep iterating through it? How about:
for s in l:
while True:
stuff()
# use a "break" instead of s = i.next()
看起来好像很近到你想要的?对于您的代码示例,它将是:
Does that seem like something close to what you would want? With your code example, it would be:
for s in some_list:
while True:
if state is STATE_CODE:
if "//" in s:
tokens.add( TOKEN_COMMENT, s.split( "//" )[1] )
state = STATE_COMMENT
else :
tokens.add( TOKEN_CODE, s )
if state is STATE_COMMENT:
if "//" in s:
tokens.append( TOKEN_COMMENT, s.split( "//" )[1] )
break # get next s
else:
state = STATE_CODE
# re-evaluate same line
# continues automatically
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