Python 在迭代时,zip和izip之间有什么功能上的区别吗?
我有如下代码:Python 在迭代时,zip和izip之间有什么功能上的区别吗?,python,iterator,Python,Iterator,我有如下代码: for v1, v2 in zip(iter1, iter2): print len(v1) # prints 0 但当我将zip改为itertools.izip时,它会打印1 for v1, v2 in izip(iter1, iter2): print len(v1) # prints 1 其他代码都是一样的。我只是用izip替换了zip,它工作了。izip的输出是正确的 编辑:添加整个代码: #!/bin/python """ How to use: &g
for v1, v2 in zip(iter1, iter2):
print len(v1) # prints 0
但当我将zip改为itertools.izip时,它会打印1
for v1, v2 in izip(iter1, iter2):
print len(v1) # prints 1
其他代码都是一样的。我只是用izip替换了zip,它工作了。izip的输出是正确的
编辑:添加整个代码:
#!/bin/python
"""
How to use:
>>> from color_assign import Bag, assign_colors
>>> from pprint import pprint
>>> old_topics = set([
... Bag(name='T1', group=0, color=1, count=16000),
... Bag(name='T2', group=0, color=1, count=16000),
... Bag(name='T3', group=1, color=2, count=16000),
... Bag(name='T4', group=2, color=3, count=16000),
... ])
>>> new_topics = set([
... Bag(name='T1', group=0, color=None, count=16000),
... Bag(name='T2', group=4, color=None, count=16000),
... Bag(name='T3', group=1, color=None, count=16000),
... Bag(name='T4', group=1, color=None, count=16000),
... ])
>>> color_ranges = [ [1,10] ]
>>> assign_colors(old_topics, new_topics, color_ranges)
>>> pprint(sorted(new_topics, key=attrgetter('name')))
[Bag(name=T1, group=0, color=1, count=16000),
Bag(name=T2, group=4, color=3, count=16000),
Bag(name=T3, group=1, color=2, count=16000),
Bag(name=T4, group=1, color=2, count=16000)]
>>>
"""
from itertools import groupby, izip
from operator import attrgetter
class Bag:
def __init__(self, name, group, color=None, count=None):
self.name = name
self.group = group
self.color = color
self.count = count
def __repr__(self):
return "Bag(name={self.name}, group={self.group}, color={self.color}, count={self.count})".format(self=self)
def __key(self):
return self.name
def __hash__(self):
return hash(self.__key())
def __eq__(self, other):
return type(self) is type(other) and self.__key() == other.__key()
def color_range_gen(color_ranges, used_colors):
color_ranges = sorted(color_ranges)
color_iter = iter(sorted(used_colors))
next_used = next(color_iter, None)
for start_color, end_color in color_ranges:
cur_color = start_color
end_color = end_color
while cur_color <= end_color:
if cur_color == next_used:
next_used = next(color_iter, None)
else:
yield cur_color
cur_color = cur_color + 1
def assign_colors(old_topics, new_topics, color_ranges):
old_topics -= (old_topics-new_topics) #Remove topics from old_topics which are no longer present in new_topics
used_colors = set()
def group_topics(topics):
by_group = attrgetter('group')
for _, tgrp in groupby(sorted(topics, key=by_group), by_group):
yield tgrp
for topic_group in group_topics(old_topics):
oldtset = frozenset(topic_group)
peek = next(iter(oldtset))
try:
new_group = next(topic.group for topic in new_topics if topic.name == peek.name and not topic.color)
except StopIteration:
continue
newtset = frozenset(topic for topic in new_topics if topic.group == new_group)
if oldtset <= newtset:
for topic in newtset:
topic.color = peek.color
used_colors.add(peek.color)
free_colors = color_range_gen(color_ranges, used_colors)
unassigned_topics = (t for t in new_topics if not t.color)
for tset, color in zip(group_topics(unassigned_topics), free_colors):
for topic in tset:
topic.color = color
if __name__ == '__main__':
import doctest
doctest.testmod()
更新:
问题在于
groupby
在使用zip时使迭代器无效是的,它们的输出是相同的。唯一的区别是zip
在内存中创建一个列表,而izip
返回一个迭代器
>>> from itertools import izip
>>> zip(range(5), 'abcde')
[(0, 'a'), (1, 'b'), (2, 'c'), (3, 'd'), (4, 'e')]
>>> it = izip(range(5), 'abcde')
>>> it
<itertools.izip object at 0xa660fcc>
>>> next(it)
(0, 'a')
>>> next(it)
(1, 'b')
>>来自itertools导入izip
>>>邮政编码(范围(5),“abcde”)
[(0,'a'),(1,'b'),(2,'c'),(3,'d'),(4,'e')]
>>>它=izip(范围(5),‘abcde’)
>>>它
>>>下一个(it)
(0,‘a’)
>>>下一个(it)
(1,‘b’)
请注意,
izip
在Python3中已被删除,zip
在那里返回一个iterator
您遇到的问题是由两个因素共同造成的。首先,izip
仅根据需要推进底层迭代器,而zip
需要立即获取所有项。其次,当一个groupby
对象处于高级状态时:
返回的组本身是一个迭代器,它与groupby()
共享底层iterable。因为源是共享的,所以当groupby()
对象处于高级状态时,前面的组将不再可见。因此,如果以后需要该数据,则应将其存储为列表:
作为一个简单的修复,您可以更改
group\u主题
,在生成组之前调用其组上的list
。您的错误在其他地方。给我们看看。特别是,包括创建iter1
和iter2
,不要在应该使用izip
的代码中调用zip
@user2357112将可运行代码粘贴到testcase。如果您将zip更改为iziprelated,测试用例将通过:有人能发现这个bug吗?希望我的电脑没有问题。我想不出for loop
是如何影响发电机的。我只更改for循环中的当前项。根本不引用循环的迭代。@balki:进一步分析了代码。见扩展答案。mera he+1 yad rakhiyo
>>> from itertools import izip
>>> zip(range(5), 'abcde')
[(0, 'a'), (1, 'b'), (2, 'c'), (3, 'd'), (4, 'e')]
>>> it = izip(range(5), 'abcde')
>>> it
<itertools.izip object at 0xa660fcc>
>>> next(it)
(0, 'a')
>>> next(it)
(1, 'b')