Enumerate in nested for loop with list comprehension for outer increment

Question

I am trying to apply the accepted solution to this question to the problem below but stupidly I cannot:

In:

increment='increment'
[f'{level_A}_{level_B}_{level_C}_{increment}' 
for level_A, rng in [(5, list(range(1,3))), (6, list(range(1,3)))]
for level_B in rng
for level_C in range(1, 5)]

Out:

['5_1_1_increment',
 '5_1_2_increment',
 '5_1_3_increment',
 '5_1_4_increment',
 '5_2_1_increment',
 '5_2_2_increment',
 '5_2_3_increment',
 '5_2_4_increment',
 '6_1_1_increment',
 '6_1_2_increment',
 '6_1_3_increment',
 '6_1_4_increment',
 '6_2_1_increment',
 '6_2_2_increment',
 '6_2_3_increment',
 '6_2_4_increment']

Where the increment values need to be 1,2,3,..15,16. Importantly, I need to do this in a single line (ie no variable definition outside the comprehension) and ideally without any imports (like in the original question's accepted answer)

Answer 1

Since you need to number them after you generate the combinations, you need to use nested generators/comprehensions:

• in the inner one, generate the combinations;
• number them from 1, using enumerate(..., start=1)
• in the outer one, format them up in the required form.

[
    f"{level_A}_{level_B}_{level_C}_{increment}"
    for increment, (level_A, level_B, level_C) in enumerate(
        (
            (A, B, C)
            for A, rng in [(5, list(range(1, 3))), (6, list(range(1, 3)))]
            for B in rng
            for C in range(1, 5)
        ),
        start=1,
    )
]

Answer 2

Use walrus operator for increment.

>>> increment=0
>>> [f'{level_A}_{level_B}_{level_C}_{(increment:=increment+1)}' 
... for level_A, rng in [(5, list(range(1,3))), (6, list(range(1,3)))]
... for level_B in rng
... for level_C in range(1, 5)]

which gives me:

['5_1_1_1', '5_1_2_2', '5_1_3_3', '5_1_4_4', '5_2_1_5', '5_2_2_6', '5_2_3_7', '5_2_4_8', '6_1_1_9', '6_1_2_10', '6_1_3_11', '6_1_4_12', '6_2_1_13', '6_2_2_14', '6_2_3_15', '6_2_4_16']