How to get the Cartesian product of multiple lists

Question

How can I get the Cartesian product (every possible combination of values) from a group of lists?

For example, given

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

How do I get this?

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

---

_{One common application for this technique is to avoid deeply nested loops. See Avoiding nested for loops for a more specific duplicate. Similarly, this technique might be used to "explode" a dictionary with list values; see Combine Python Dictionary Permutations into List of Dictionaries .}

_{If you want a Cartesian product of the same list with itself multiple times, itertools.product can handle that elegantly. See Operation on every pair of element in a list or How can I get "permutations with repetitions" from a list (Cartesian product of a list with itself)?.}

_{Many people who already know about itertools.product struggle with the fact that it expects separate arguments for each input sequence, rather than e.g. a list of lists. The accepted answer shows how to handle this with *. However, the use of * here to unpack arguments is fundamentally not different from any other time it's used in a function call. Please see Expanding tuples into arguments for this topic (and use that instead to close duplicate questions, as appropriate).}

Answer 1

Use itertools.product, which has been available since Python 2.6.

import itertools

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

This is the same as:

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