如何模拟一个do-while循环?

我需要在Python程序中模拟一个do-while循环。不幸的是，下面的简单代码不能工作:

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"

不是"1,2,3,done"，而是输出如下:

[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”异常并中断一段时间，我能做些什么循环正常吗?

下面的伪代码显示了为什么需要这样一个东西的示例。

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

当前回答

用于包含try语句的do - while循环

loop = True
while loop:
    generic_stuff()
    try:
        questionable_stuff()
#       to break from successful completion
#       loop = False  
    except:
        optional_stuff()
#       to break from unsuccessful completion - 
#       the case referenced in the OP's question
        loop = False
   finally:
        more_generic_stuff()

或者，当不需要'finally'从句时

while True:
    generic_stuff()
    try:
        questionable_stuff()
#       to break from successful completion
#       break  
    except:
        optional_stuff()
#       to break from unsuccessful completion - 
#       the case referenced in the OP's question
        break

2011-05-10 22:03:06

其他回答

While循环:

while condition:
  print("hello")

执行while循环:

while True:
  print("hello")
  if not condition:
    break

你也可以使用任何真布尔值作为条件:

while 1:
  print("hello")
  if not condition:
    break

另一个变体:

check = 1
while check:
    print("hello")
    check = condition

2022-03-03 17:51:03

while condition is True: 
  stuff()
else:
  stuff()

2010-11-30 01:38:03

内置的iter函数具体做到了这一点:

for x in iter(YOUR_FN, TERM_VAL):
    ...

例如(在Py2和3中测试过):

class Easy:
  X = 0
  @classmethod
  def com(cls):
    cls.X += 1
    return cls.X

for x in iter(Easy.com, 10):
  print(">>>", x)

如果你想给出一个终止条件而不是一个值，你总是可以设置一个等式，并要求这个等式为True。

2020-06-28 19:00:48

看看这是否有帮助:

在异常处理程序中设置一个标志，并在处理s之前检查它。

flagBreak = false;
while True :

    if flagBreak : break

    if s :
        print s
    try :
        s = i.next()
    except StopIteration :
        flagBreak = true

print "done"

2009-04-13 08:17:55

你想知道:

为了捕捉“停止迭代”异常并正确地打破while循环，我能做些什么?

你可以这样做，如下所示，这也利用了Python 3.8中引入的赋值表达式特性(又名“海象运算符”):

list_of_ints = [1, 2, 3]
iterator = iter(list_of_ints)

try:
    while (element := next(iterator)):
        print(element)
except StopIteration:
    print("done")

另一种可能(从Python 2.6到3.x都适用)是为内置的next()函数提供一个默认参数，以避免StopIteration异常:

SENTINEL = object()  # Unique object.
list_of_ints = [1, 2, 3]
iterator = iter(list_of_ints)

while True:
    element = next(iterator, SENTINEL)
    if element is SENTINEL:
        break
    print(element)

print("done")

2021-03-13 18:36:04

如何模拟一个do-while循环?

推荐文章

最新文章

标签