如何模拟 do-while 循环? [英] How to emulate a do-while loop?

问题描述

我需要在 Python 程序中模拟 do-while 循环.不幸的是，以下简单的代码不起作用:

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"

它输出的不是1,2,3,done"，而是以下输出:

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
']

我该怎么做才能捕获停止迭代"异常并暂停一段时间正确循环?

What can I do in order to catch the 'stop iteration' exception and break a while loop properly?

为什么可能需要这样的东西的示例如下所示为伪代码.

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 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

或者:

stuff()
while not fail_condition:
  stuff()

你在做什么尝试使用 do while 循环打印列表中的内容?为什么不直接使用:

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:

所以你有行列表吗?你想继续迭代它吗?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()

这看起来与您想要的很接近吗?使用您的代码示例，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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