Question

If I have, for example, a list of tuples such as

a = [(1,2)] * 4

how would I create a list of the first element of each tuple? That is, [1, 1, 1, 1].

Answer 1

Use a list comprehension:

>>> a = [(1,2)] * 4
>>> [t[0] for t in a]
[1, 1, 1, 1]

You can also unpack the tuple:

>>> [first for first,second in a]
[1, 1, 1, 1]

If you want to get fancy, combine map and operator.itemgetter. In python 3, you’ll have to wrap the construct in list to get a list instead of an iterable:

>>> import operator
>>> map(operator.itemgetter(0), a)
<map object at 0x7f3971029290>
>>> list(map(operator.itemgetter(0), a))
[1, 1, 1, 1]