Python: Anyway to use map to get first element of a tuple

Question

I have a tuple of tuples and I want to put the first value in each of the tuples into a set. I thought using map() would be a good way of doing this the only thing is I can't find an easy way to access the first element in the tuple. So for example I have the tuple ((1,), (3,)). I'd like to do something like set(map([0], ((1,), (3,)))) (where [0] is accessing the zeroth element) to get a set with 1 and 3 in it. The only way I can figure to do it is to define a function: def first(t): return t[0]. Is there anyway of doing this in one line without having to declare the function?

Answer 1

Use a list comprehension:

data = ((1,), (3,))
print([x[0] for x in data])

Answer 2

Use operator.itemgetter:

from operator import itemgetter
map(itemgetter(0), ((1,), (3,)))

While the list comprehensions are generally more readable, itemgetter is closest to what you asked for. It's also a bit faster:

>>> from timeit import timeit
>>> setup = 'from operator import itemgetter; lst=( ("a",), ("b",), (1,), (2,))'
>>> timeit('map(itemgetter(0), lst)', setup=setup)
0.13061050399846863
>>> timeit('[i[0] for i in lst]', setup=setup)
0.20302422800159547

Answer 3

my_set = {x[0] for x in TUPLES}

Answer 4

Just another way to get it:

set(x for x, in data)