How Can I Efficiently Compute the Cartesian Product of Lists in Python?

Computing the Cartesian Product of Lists

Obtaining the Cartesian product, or all possible combinations of values, from multiple lists poses a common challenge in programming. Consider the example of a list of lists:

somelists = [
   [1, 2, 3],
   ['a', 'b'],
   [4, 5]
]

The Ideal Output:

The result we seek is a single list containing every possible combination of values from the input lists:

[(1, 'a', 4), (1, 'a', 5), (1, 'b', 4), (1, 'b', 5), (2, 'a', 4), (2, 'a', 5), ...]

The Pythonic Solution: itertools.product

The Python standard library provides a powerful tool for this task: itertools.product. Available since Python 2.6, this function expects the input sequences as separate arguments.

import itertools

for element in itertools.product(*somelists):
    print(element)

Alternatively, you can explicitly specify each sequence as an argument:

for element in itertools.product([1, 2, 3], ['a', 'b'], [4, 5]):
    print(element)

itertools.product will return a generator object that yields each combination as a tuple. To obtain the desired list, you can iterate over the generator and convert each tuple to a list if needed.

By utilizing itertools.product, you can efficiently compute the Cartesian product of multiple lists, avoiding the need for nested loops and ensuring a concise and readable solution to this common programming challenge.

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