An elegant and fast way to consecutively iterate over two or more containers in Python?

Question

I have three collection.deques and what I need to do is to iterate over each of them and perform the same action:

for obj in deque1:  
    some_action(obj)           


        

Answer 1

Depending on what order you want to process the items:

import itertools

for items in itertools.izip(deque1, deque2, deque3):
    for item in items:
        some_action(item)

for item in itertools.chain(deque1, deque2, deque3):
    some_action(item)

I'd recommend doing this to avoid hard-coding the actual deques or number of deques:

deques = [deque1, deque2, deque3]
for item in itertools.chain(*deques):
    some_action(item)

To demonstrate the difference in order of the above methods:

>>> a = range(5)
>>> b = range(5)
>>> c = range(5)
>>> d = [a, b, c]
>>>
>>> for items in itertools.izip(*d):
...     for item in items:
...         print item,
...
0 0 0 1 1 1 2 2 2 3 3 3 4 4 4
>>>
>>> for item in itertools.chain(*d):
...     print item,
...
0 1 2 3 4 0 1 2 3 4 0 1 2 3 4
>>>