python – Access item in a list of lists

python – Access item in a list of lists

You can access the elements in a list-of-lists by first specifying which list youre interested in and then specifying which element of that list you want. For example, 17 is element 2 in list 0, which is list1[0][2]:

>>> list1 = [[10,13,17],[3,5,1],[13,11,12]]
>>> list1[0][2]
17

So, your example would be

50 - list1[0][0] + list1[0][1] - list1[0][2]

You can use itertools.cycle:

>>> from itertools import cycle
>>> lis = [[10,13,17],[3,5,1],[13,11,12]]
>>> cyc = cycle((-1, 1))
>>> 50 + sum(x*next(cyc) for x in lis[0])   # lis[0] is [10,13,17]
36

Here the generator expression inside sum would return something like this:

>>> cyc = cycle((-1, 1))
>>> [x*next(cyc) for x in lis[0]]
[-10, 13, -17]

You can also use zip here:

>>> cyc = cycle((-1, 1))
>>> [x*y for x, y  in zip(lis[0], cyc)]
[-10, 13, -17]

python – Access item in a list of lists

List1 = [[10,-13,17],[3,5,1],[13,11,12]]

num = 50
for i in List1[0]:num -= i
print num

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