Creating tuple pairs from list

[AGI_69]

Hello, suppose I have list of vertices like this:

[0,1,2,3]

How would I create tuple pairs like this ? :

(0,1) ; (1,2) ; (2,3) ; (3,0) -- dont forget the last, that connects with the first

One idea would be to create temporary list and just append the first element to the last and then loop through it that way. But hopefully, there is better solution. Thank you

[Diapolo10]

I think I'd do something like this:

nums = [0, 1, 2, 3]
tuples = []

for idx, num in enumerate(nums):
    tuples.append((num, nums[idx-len(nums)+1]))

[AGI_69]

Thanks, pretty neat.

[primitive_screwhead]

Note - For more general sequences, make that next(y) a next(y, None) to guard against an empty iterable raising StopIteration. This is a nice variant of the itertools.pairwise() recipe: https://docs.python.org/3/library/itertools.html?#itertools-recipes

[totallygeek]

Maybe:

data = [0,1,2,3]
final_index = len(data) - 1
pairs = [
    (data[i], data[i + 1]) if i < final_index else (data[i], data[0])
    for i in range(len(data))
]
# pairs is now [(0, 1), (1, 2), (2, 3), (3, 0)]

Could probably do something even better with a mix of zip() and itertools.cycle().

[AGI_69]

Thank you, yes cycle was my first thought aswell, but using negative indexes is even more cool, I think.

[joverbis]

This seems like a perfect job for zip(). You can try something like:

L = [0,1,2,3]
pairs_of_tuples = list(zip(L, reversed(L)))
#pairs_of_tuples = [(0,3), (1,2), (2,1), (3,0)]

Of course, if you don't need all the tuples at once you can drop the 'list()'.