[英]Python How to I check if last element has been reached in iterator tool chain?
for elt in itertools.chain.from_iterable(node):
if elt is the last element:
do statement
我如何实现这一目标
您可以使用iter.next()
在 while 循环中手动推进迭代器,然后捕获StopIteration
异常:
>>> from itertools import chain
>>> it = chain([1,2,3],[4,5,6],[7,8,9])
>>> while True:
... try:
... elem = it.next()
... except StopIteration:
... print "Last element was:", elem, "... do something special now"
... break
... print "Got element:", elem
...
...
Got element: 1
Got element: 2
Got element: 3
Got element: 4
Got element: 5
Got element: 6
Got element: 7
Got element: 8
Got element: 9
Last element was: 9 ... do something special now
>>>
当循环结束时, elt
变量不会超出范围,并且仍然保存循环给它的最后一个值。 所以你可以把代码放在循环的末尾,然后对elt
变量进行操作。 它不是很漂亮,但是 Python 的作用域规则也不是很漂亮。
唯一的问题(感谢 cvondrick)是循环可能永远不会执行,这意味着elt
不存在 - 我们会得到一个NameError
。 因此,完整的方法大致是:
del elt # not necessary if we haven't use elt before, but just in case
for elt in itertools.chain.from_iterable(node):
do_stuff_to_each(elt)
try:
do_stuff_to_last(elt)
except NameError: # no last elt to do stuff to
pass
我做这样的事情:
rng = len(mlist)
for i in range(rng):
foo = mlist[i]
foo.do_something_for_every_item_regardless()
if i == rng - 1: #since we go from 0 to rng-1
foo.last_item_only_operation()
你本身不能。 您需要存储当前项目、推进迭代器并捕获StopIteration
异常。 然后你需要以某种方式表明你有最后一个项目。
while True:
try:
print(next(myIterator))
except StopIteration:
break
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