python-获取元组列表第一个索引？

Question

返回以下内容的最简洁的方法是什么：

给定一个元组列表，返回一个由元组第一个（或第二个，无关紧要）元素组成的列表。

致：

[(1,'one'),(2,'two'),(3,'three')]

返回的列表将是

[1,2,3]

Answer 1

>>> tl = [(1,'one'),(2,'two'),(3,'three')]
>>> [item[0] for item in tl]
[1, 2, 3]

Answer 2

>>> mylist = [(1,'one'),(2,'two'),(3,'three')]
>>> [j for i,j in mylist]
['one', 'two', 'three']
>>> [i for i,j in mylist]
[1, 2, 3]

这是使用list comprehension (have a look at this link)。因此它遍历mylist中的元素，依次将i和j设置为元组中的两个元素。它实际上相当于：

>>> newlist = []
>>> for i, j in mylist:
...     newlist.append(i)
... 
>>> newlist
[1, 2, 3]

Answer 3

如果两者都需要，请使用zip

>>> r=(1,'one'),(2,'two'),(3,'three')
>>> zip(*r)
[(1, 2, 3), ('one', 'two', 'three')]