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Is there a clever way to iterate over two lists in Python (without using list comprehension)?
I mean, something like this:
# (a, b) is the cartesian product between the two lists' elements
for a, b in list1, list2:
foo(a, b)
instead of:
for a in list1:
for b in list2:
foo(a, b)
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Example 2: Using itertools (Python 2+)Using the zip_longest() method of itertools module, you can iterate through two parallel lists at the same time. The method lets the loop run until the longest list stops.
We can iterate through a list by using the range() function and passing the length of the list. It will return the index from 0 till the end of the list.
You can loop through the list items by using a while loop. Use the len() function to determine the length of the list, then start at 0 and loop your way through the list items by referring to their indexes. Remember to increase the index by 1 after each iteration.
Iterating over a list can also be achieved using a while loop. The block of code inside the loop executes until the condition is true. A loop variable can be used as an index to access each element.
itertools.product() does exactly this:
for a, b in itertools.product(list1, list2):
foo(a, b)
It can handle an arbitrary number of iterables, and in that sense is more general than nested for loops.
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