[英]python: most elegant way to intersperse a list with an element
Input:输入:
intersperse(666, ["once", "upon", "a", 90, None, "time"])
Output: Output:
["once", 666, "upon", 666, "a", 666, 90, 666, None, 666, "time"]
What's the most elegant (read: Pythonic) way to write intersperse
?编写
intersperse
的最优雅(阅读:Pythonic)方式是什么?
I would have written a generator myself, but like this:我会自己写一个生成器,但像这样:
def joinit(iterable, delimiter):
it = iter(iterable)
yield next(it)
for x in it:
yield delimiter
yield x
itertools
to the rescue itertools
来救援
- or - - 或者 -
How many itertools functions can you use in one line?一行可以使用多少个 itertools 函数?
from itertools import chain, izip, repeat, islice
def intersperse(delimiter, seq):
return islice(chain.from_iterable(izip(repeat(delimiter), seq)), 1, None)
Usage:用法:
>>> list(intersperse(666, ["once", "upon", "a", 90, None, "time"])
["once", 666, "upon", 666, "a", 666, 90, 666, None, 666, "time"]
Another option that works for sequences:另一个适用于序列的选项:
def intersperse(seq, value):
res = [value] * (2 * len(seq) - 1)
res[::2] = seq
return res
Solution is trivial using more_itertools.intersperse
:使用
more_itertools.intersperse
解决方案很简单:
>>> from more_itertools import intersperse
>>> list(intersperse(666, ["once", "upon", "a", 90, None, "time"]))
['once', 666, 'upon', 666, 'a', 666, 90, 666, None, 666, 'time']
Technically, this answer isn't "writing" intersperse
, it's just using it from another library.从技术上讲,这个答案不是“写作”
intersperse
,它只是从另一个库中使用它。 But it might save others from having to reinvent the wheel.但这可能会使其他人不必重新发明轮子。
I would go with a simple generator.我会用一个简单的发电机。
def intersperse(val, sequence):
first = True
for item in sequence:
if not first:
yield val
yield item
first = False
and then you can get your list like so:然后你可以像这样得到你的列表:
>>> list(intersperse(666, ["once", "upon", "a", 90, None, "time"]))
['once', 666, 'upon', 666, 'a', 666, 90, 666, None, 666, 'time']
alternatively you could do:或者你可以这样做:
def intersperse(val, sequence):
for i, item in enumerate(sequence):
if i != 0:
yield val
yield item
I'm not sure which is more pythonic我不确定哪个更 pythonic
def intersperse(word,your_list):
x = [j for i in your_list for j in [i,word]]
>>> intersperse(666, ["once", "upon", "a", 90, None, "time"])
['once', 666, 'upon', 666, 'a', 666, 90, 666, None, 666, 'time', 666]
[Edit] Corrected code below: [编辑]更正以下代码:
def intersperse(word,your_list):
x = [j for i in your_list for j in [i,word]]
x.pop()
return x
>>> intersperse(666, ["once", "upon", "a", 90, None, "time"])
['once', 666, 'upon', 666, 'a', 666, 90, 666, None, 666, 'time']
I just came up with this now, googled to see if there was something better... and IMHO there wasn't :-)我现在才想到这个,用谷歌搜索看看是否有更好的东西......恕我直言没有:-)
def intersperse(e, l):
return list(itertools.chain(*[(i, e) for i in l]))[0:-1]
I believe this one looks pretty nice and easy to grasp compared to the yield next(iterator)
or itertools.iterator_magic()
one :)我相信与
yield next(iterator)
或itertools.iterator_magic()
one 相比,这个看起来非常漂亮且易于掌握:)
def list_join_seq(seq, sep):
for i, elem in enumerate(seq):
if i > 0: yield sep
yield elem
print(list(list_join_seq([1, 2, 3], 0))) # [1, 0, 2, 0, 3]
Dunno if it's pythonic, but it's pretty simple:不知道它是否是 pythonic,但它非常简单:
def intersperse(elem, list):
result = []
for e in list:
result.extend([e, elem])
return result[:-1]
How about:怎么样:
from itertools import chain,izip_longest
def intersperse(x,y):
return list(chain(*izip_longest(x,[],fillvalue=y)))
The basic and easy you could do is:您可以做的基本且简单的事情是:
a = ['abc','def','ghi','jkl']
# my separator is : || separator ||
# hack is extra thing : --
'--|| separator ||--'.join(a).split('--')
output:输出:
['abc','|| separator ||','def','|| separator ||','ghi','|| separator ||','jkl']
This works:这有效:
>>> def intersperse(e, l):
... return reduce(lambda x,y: x+y, zip(l, [e]*len(l)))
>>> intersperse(666, ["once", "upon", "a", 90, None, "time"])
('once', 666, 'upon', 666, 'a', 666, 90, 666, None, 666, 'time', 666)
If you don't want a trailing 666
, then return reduce(...)[:-1]
.如果您不想要尾随
666
,则return reduce(...)[:-1]
。
Seems general and efficient:似乎通用且高效:
def intersperse(lst, fill=...):
"""
>>> list(intersperse([1,2,3,4]))
[1, Ellipsis, 2, Ellipsis, 3, Ellipsis, 4]
"""
return chain(*zip(lst[:-1], repeat(fill)), [lst[-1]])
You can use Python's list comprehension:您可以使用 Python 的列表理解:
def intersperse(iterable, element):
return [iterable[i // 2] if i % 2 == 0 else element for i in range(2 * len(iterable) - 1)]
def intersperse(items, delim):
i = iter(items)
return reduce(lambda x, y: x + [delim, y], i, [i.next()])
Should work for lists or generators.应该适用于列表或生成器。
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