How to Iterate Through Two Lists in Parallel

Given two lists, a common task is to iterate through them in pairs. While iterating over indices is a feasible approach, it may not be the most Pythonic solution.

Python 3 Solution

In Python 3, the zip() function returns an iterator of tuples, making it an efficient and concise way to iterate through multiple iterables in parallel. The syntax is:

for element_1, element_2 in zip(iterable_1, iterable_2):
    ...

for f, b in zip(foo, bar):
    print(f, b)

Python 2 Solution

In Python 2, zip() returns a list of tuples, which can be inefficient for large datasets. To avoid creating unnecessary temporary variables, consider using itertools.izip() for an iterator instead:

import itertools
for f, b in itertools.izip(foo, bar):
    print(f, b)

If desired, itertools.izip_longest() can be used to iterate until both iterables are exhausted, filling in missing values with the specified fill value (or None by default).

Key Points

• The zip() function can iterate through multiple iterables simultaneously.
• In Python 3, zip() returns an iterator of tuples.
• In Python 2, zip() returns a list of tuples, while itertools.izip() and itertools.izip_longest() provide iterators for efficiency.