Python：在嵌套字典中循环并组合值

Question

I am creating a nested dictionary that describes several cases ('1ql' and '2ql'), each with a different number of variations ('var0', 'var1', ...). I use dict comprehension in the following manner:

from numpy import random as rnd

QLS = {
    key: {
        idx: rad
        for idx, rad in enumerate(['var{}'.format(i) for i in range(rnd.randint(1, 4))])
        }
    for key in ['1ql', '2ql']
    }

This works great, but I have been struggling with the how to handle the dictionary for saving to file(s). I would like to iterate over each variation of '1ql', and then iterate simultaneously over each iteration of '2ql'. This can easily be accomplished like this:

for key1, val1 in QLS['1ql'].items():
    for key2, val2 in QLS['2ql'].items():
        print('1ql: {}, 2ql: {}'.format(val1, val2))

which, for 2 variations of '1ql' and 3 variation '2ql', produces 6 total permutations:

1ql: var0, 2ql: var0
1ql: var0, 2ql: var1
1ql: var0, 2ql: var2
1ql: var1, 2ql: var0
1ql: var1, 2ql: var1
1ql: var1, 2ql: var2

However, I would like to get this automatically for any number of cases, for any number of variations per case, without having to specify these by hand. I have tried different iteration schemes and even by inverting the inner and outer keys, but to no avail.

I would really like the to learn the most pythonic way to accomplish this. Thanks!

Answer 1

First, transform the data to remove the parts we don't need:

x = [[(case, var) for var in QLS[case].values()] for case in QLS.keys()]

Now x is something like:

[[('1ql', 'var0'), ('1ql', 'var1'), ('1ql', 'var2')],
 [('2ql', 'var0'), ('2ql', 'var1'), ('2ql', 'var2')]]

Finally, use itertools.product() to get the result:

list(itertools.product(*x))

Probably in your real code you'll iterate over the results and use print() on each one to get the format you need, but wrapping with list() as above gives you an idea:

[(('1ql', 'var0'), ('2ql', 'var0')),
 (('1ql', 'var0'), ('2ql', 'var1')),
 (('1ql', 'var0'), ('2ql', 'var2')),
 (('1ql', 'var1'), ('2ql', 'var0')),
 (('1ql', 'var1'), ('2ql', 'var1')),
 (('1ql', 'var1'), ('2ql', 'var2')),
 (('1ql', 'var2'), ('2ql', 'var0')),
 (('1ql', 'var2'), ('2ql', 'var1')),
 (('1ql', 'var2'), ('2ql', 'var2'))]