CODEWITHSUNDEEP
pythonlistpython-itertools
Daniel
Daniel

Reputation: 691

Python Iteration Through Lists with Stepped Progression

Given the following lists:

letters = ('a', 'b', 'c', 'd', 'e', 'f', 'g')
numbers = ('1', '2', '3', '4')

How can I produce an iterated list that produces the following:

output = [('a', '1'), ('b', '2'), ('c', '3'), ('d', '4'), 
          ('e', '1'), ('f', '2'), ('g', '3'), ('a', '4'),
          ('b', '1'), ('c', '2'), ('d', '3'), ('e', '4'),
          ('f', '1'), ('g', '2')...]

I feel like I should be able to produce the desired output by using 

output = (list(zip(letters, itertools.cycle(numbers))

But this produces the following:

output = [('a', '1'), ('b', '2'), ('c', '3'), ('d', '4'),
          ('e', '1'), ('f', '2'), ('g', '3')]

Any help would be greatly appreciated.

Upvotes: 1

Views: 59

Answers (2)

Philipp Claßen
Philipp Claßen

Reputation: 44009

If you want a finite list of elements, this should work

import itertools

letters = ('a', 'b', 'c', 'd', 'e', 'f', 'g')
numbers = ('1', '2', '3', '4')
max_elems = 10

list(itertools.islice((zip(itertools.cycle(letters), itertools.cycle(numbers))), max_elems))

results in

[('a', '1'), ('b', '2'), ('c', '3'), ('d', '4'), ('e', '1'), ('f', '2'), ('g', '3'), ('a', '4'), ('b', '1'), ('c', '2')]

Upvotes: 0

Uriel
Uriel

Reputation: 16204

If you are looking for an infinite generator, you can use cycle with zip for both lists, in the form of zip(itertools.cycle(x), itertools.cycle(y)). That would supply you with the required generator:

>>> for x in zip(itertools.cycle(letters), itertools.cycle(numbers)):
...     print(x)
...
('a', '1')
('b', '2')
('c', '3')
('d', '4')
('e', '1')
('f', '2')
('g', '3')
('a', '4')
('b', '1')
('c', '2')
('d', '3')
...

Upvotes: 1

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