Python:在列表对的一个成员中查找顺序更改，然后报告其他 [英] Python: find sequential change in one member of list pairs, report other

问题描述

必须有一种更简单，更Python化的方式来做到这一点.

There must be a simpler, more pythonic way of doing this.

给出以下配对列表:

pp = [('a',1),('b',1),('c',1),('d',2),('e',2)]

我如何最轻松地在第二对项目发生变化的相邻对中找到第一项(这里是从1到2).因此，我正在寻找['c'，'d'].假设整个列表的pair [1]中只有一个更改，但是它可能是字符串.

How do I most easily find the first item in adjacent pairs where the second item changes (here, from 1 to 2). Thus I'm looking for ['c','d']. Assume there will only be one change in pair[1] for the entire list, but that it may be a string.

此代码有效，但冗长且繁琐.

This code works but seems excruciatingly long and cumbersome.

for i, pair in enumerate(pp):
    if i == 0: 
        pInitial = pair[0] 
        sgInitial = pair[1]
    pNext = pair[0]
    sgNext = pair[1]
    if sgInitial == sgNext:
        sgInitial = sgNext
        pInitial = pNext
    else:
        pOne = pInitial
        pTwo = pNext
        x = [pOne, pTwo]
        print x
        break

谢谢 蒂姆

推荐答案

import itertools as it

pp = [('a',1),('b',1),('c',1),('d',2),('e',2)]

# with normal zip and slicing
for a,b in zip(pp,pp[1:]):
    if a[1] != b[1]:
        x=(a[0],b[0])
        print x
        break
# with generators and izip
iterfirst = (b for a,b in pp)
itersecond = (b for a,b in pp[1:])
iterfirstsymbol = (a for a,b in pp)
itersecondsymbol = (a for a,b in pp[1:])
iteranswer = it.izip(iterfirstsymbol, itersecondsymbol, iterfirst, itersecond)

print next((symbol1, symbol2)
           for symbol1,symbol2, first, second in iteranswer
           if first != second)

添加了可读的生成器版本.

Added my readable generator version.

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