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
我不知道你想干什么。你可以像这样实现一个do-while循环:
while True:
stuff()
if fail_condition:
break
Or:
stuff()
while not fail_condition:
stuff()
你为什么要用一个do while循环来打印列表中的东西?为什么不直接使用:
for i in l:
print i
print "done"
更新:
你有台词清单吗?你想一直遍历它吗?如何:
for s in l:
while True:
stuff()
# use a "break" instead of s = i.next()
这看起来像是你想要的吗?对于您的代码示例，它将是:
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
我不知道你想干什么。你可以像这样实现一个do-while循环:
while True:
stuff()
if fail_condition:
break
Or:
stuff()
while not fail_condition:
stuff()
你为什么要用一个do while循环来打印列表中的东西?为什么不直接使用:
for i in l:
print i
print "done"
更新:
你有台词清单吗?你想一直遍历它吗?如何:
for s in l:
while True:
stuff()
# use a "break" instead of s = i.next()
这看起来像是你想要的吗?对于您的代码示例，它将是:
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
这里有一个不同模式的更疯狂的解决方案——使用协程。代码仍然非常相似，但有一个重要的区别;根本就没有退出条件!当您停止向协程提供数据时，协程(实际上是协程链)就会停止。
def coroutine(func):
"""Coroutine decorator
Coroutines must be started, advanced to their first "yield" point,
and this decorator does this automatically.
"""
def startcr(*ar, **kw):
cr = func(*ar, **kw)
cr.next()
return cr
return startcr
@coroutine
def collector(storage):
"""Act as "sink" and collect all sent in @storage"""
while True:
storage.append((yield))
@coroutine
def state_machine(sink):
""" .send() new parts to be tokenized by the state machine,
tokens are passed on to @sink
"""
s = ""
state = STATE_CODE
while True:
if state is STATE_CODE :
if "//" in s :
sink.send((TOKEN_COMMENT, s.split( "//" )[1] ))
state = STATE_COMMENT
else :
sink.send(( TOKEN_CODE, s ))
if state is STATE_COMMENT :
if "//" in s :
sink.send(( TOKEN_COMMENT, s.split( "//" )[1] ))
else
state = STATE_CODE
# re-evaluate same line
continue
s = (yield)
tokens = []
sm = state_machine(collector(tokens))
for piece in i:
sm.send(piece)
上面的代码将所有令牌收集为令牌中的元组，我假设原始代码中的.append()和.add()之间没有区别。
