python - get list of tuples first index?

Question

What\'s the most compact way to return the following:

Given a list of tuples, return a list consisting of the tuples first (or second, doesn\'t matter) elements.

Answer 1

>>> 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]

This is using a list comprehension (have a look at this link). So it iterates through the elements in mylist, setting i and j to the two elements in the tuple, in turn. It is effectively equivalent to:

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