How to split the list on the pairwise elements? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

How do you split a list into evenly sized chunks in Python?

Let us have a list, there is always an even number of elements. We must break it down by pairing. Example: list['1','2','3','4'] need 1,2 开发者_Go百科and 3,4

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>>> L = [1, 2, 3, 4]
>>> pairs = zip(L[::2], L[1::2])
>>> print pairs
[(1, 2), (3, 4)]

Hope this helps

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If you want two halfs of a list.

l = [1,2,3,4]
print l[:len(l)/2], l[len(l)/2:]
>>> [1, 2] [3, 4]

If you want split a list by pairs then your question is exact duplicate.

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You can use something like this too:

lVals = xrange(1,101)
size = len(lVals)
output = ((lVals[i], lVals[i+1] if size > i+1 else None) for i in xrange(0, size, 2))

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Adapted from: How do you split a list into evenly sized chunks?

from itertools import izip_longest
data = range(6)
data_iters = [iter(data)] * 2
pairs = izip_longest(*data_iters)
[pair for pair in pairs]
>>> [(0, 1), (2, 3), (4, 5)]

The clever part is that the two elements of data_iters refer to the same object. Izip_longest alternately consumes from the two iterators passed as arguments, but since they're referring to the same object, it effectively pairs the elements in the iterator.

I take no credit for being clever here, upvote the comment I linked to if you liked my answer. :)