Multiply string vectors in python

Question

I have dynamic number of string vectors, which I need to multiply and create an array of dicts combining all possibilities.

If the input were static, I would do it like this:

sth = {
    "param1": ["p1v1", "p1v2"],
    "param2": ["p2v1", "p2v2", "p2v3"],
    "param3": ["p3v1", "p3v2"]
}

param_sets = []

for a_top_val in sth["param1"]:
    for a_val in sth["param2"]:
        for a_bottom_val in sth["param3"]:
            param_sets.append({
                "param1": a_top_val,
                "param2": a_val,
                "param3": a_bottom_val
            })

print(param_sets)
print(len(param_sets))

This prints the combined dicts like this:

[
    {'param1': 'p1v1', 'param2': 'p2v1', 'param3': 'p3v1'},
    {'param1': 'p1v1', 'param2': 'p2v1', 'param3': 'p3v2'},
    {'param1': 'p1v1', 'param2': 'p2v2', 'param3': 'p3v1'},
    {'param1': 'p1v1', 'param2': 'p2v2', 'param3': 'p3v2'},
    {'param1': 'p1v1', 'param2': 'p2v3', 'param3': 'p3v1'},
    {'param1': 'p1v1', 'param2': 'p2v3', 'param3': 'p3v2'},
    {'param1': 'p1v2', 'param2': 'p2v1', 'param3': 'p3v1'},
    {'param1': 'p1v2', 'param2': 'p2v1', 'param3': 'p3v2'},
    {'param1': 'p1v2', 'param2': 'p2v2', 'param3': 'p3v1'},
    {'param1': 'p1v2', 'param2': 'p2v2', 'param3': 'p3v2'},
    {'param1': 'p1v2', 'param2': 'p2v3', 'param3': 'p3v1'},
    {'param1': 'p1v2', 'param2': 'p2v3', 'param3': 'p3v2'}
]

How do I make the for loops around sth dynamic?

Answer 1

Use a combination of itertools.product to get all combinations of possible values and zip() to reapply the keys to the tuples:

from itertools import product

sth = {
    "param1": ["p1v1", "p1v2"],
    "param2": ["p2v1", "p2v2", "p2v3"],
    "param3": ["p3v1", "p3v2"]
}

prod = product(*(sth[k] for k in sth))
a = [dict(zip(sth.keys(), p)) for p in prod]

print(a)

to get:

[{'param1': 'p1v1', 'param2': 'p2v1', 'param3': 'p3v1'},
{'param1': 'p1v1', 'param2': 'p2v1', 'param3': 'p3v2'},
{'param1': 'p1v1', 'param2': 'p2v2', 'param3': 'p3v1'},
{'param1': 'p1v1', 'param2': 'p2v2', 'param3': 'p3v2'},
{'param1': 'p1v1', 'param2': 'p2v3', 'param3': 'p3v1'},
{'param1': 'p1v1', 'param2': 'p2v3', 'param3': 'p3v2'},
{'param1': 'p1v2', 'param2': 'p2v1', 'param3': 'p3v1'},
{'param1': 'p1v2', 'param2': 'p2v1', 'param3': 'p3v2'},
{'param1': 'p1v2', 'param2': 'p2v2', 'param3': 'p3v1'},
{'param1': 'p1v2', 'param2': 'p2v2', 'param3': 'p3v2'},
{'param1': 'p1v2', 'param2': 'p2v3', 'param3': 'p3v1'},
{'param1': 'p1v2', 'param2': 'p2v3', 'param3': 'p3v2'}]

Answer 2

You can turn every entry in sth into a list of key-value tuples. Then you can use itertools.product to get the cartesian product of all lists and use that to create your param dictionaries:

import itertools as it

sth = {
    "param1": ["p1v1", "p1v2"],
    "param2": ["p2v1", "p2v2", "p2v3"],
    "param3": ["p3v1", "p3v2"]
}

param_tuples = (
    [(param, val) for val in values] for param, values in sth.items()
)

result = [
    dict(param_combination) for param_combination in it.product(*param_tuples)
]

result:

[{'param1': 'p1v1', 'param2': 'p2v1', 'param3': 'p3v1'},
 {'param1': 'p1v1', 'param2': 'p2v1', 'param3': 'p3v2'},
 {'param1': 'p1v1', 'param2': 'p2v2', 'param3': 'p3v1'},
 {'param1': 'p1v1', 'param2': 'p2v2', 'param3': 'p3v2'},
 {'param1': 'p1v1', 'param2': 'p2v3', 'param3': 'p3v1'},
 {'param1': 'p1v1', 'param2': 'p2v3', 'param3': 'p3v2'},
 {'param1': 'p1v2', 'param2': 'p2v1', 'param3': 'p3v1'},
 {'param1': 'p1v2', 'param2': 'p2v1', 'param3': 'p3v2'},
 {'param1': 'p1v2', 'param2': 'p2v2', 'param3': 'p3v1'},
 {'param1': 'p1v2', 'param2': 'p2v2', 'param3': 'p3v2'},
 {'param1': 'p1v2', 'param2': 'p2v3', 'param3': 'p3v1'},
 {'param1': 'p1v2', 'param2': 'p2v3', 'param3': 'p3v2'}]

Answer 3

To loop dictionaries in python you can use

for k, v in sth:
    print (k, v)