python all possible pairs of 2 list elements, and getting the index of that pair

And to complete the answer and stay in the example:

import itertools  a = [1, 2, 3]b = [4, 5, 6]c = list(itertools.product(a, b))idx = c.index((1,4))

But this will be the zero-based list index, so 0 instead of 1.

python list tuples cartesian-product

One way to do this:

Find the first element of the pair your are looking for in the first list:
```
p = (1, 4)i = a.index(p[0])
```
Find the second element of the pair your are looking for in the second list:
```
j = b.index(p[1])
```
Compute the index in the product list:
```
k = i * len(b) + j
```

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