Convert a list of tuples to a dictionary

Question

I have a list of tuples with three elements:

A = [[(72, 1, 2), (96, 1, 4)], 
     [(72, 2, 1), (80, 2, 4)], 
     [], 
     [(96, 4, 1), (80, 4, 2), (70, 4, 5)],
     [(70, 5, 4)],
     ]

I need to convert it to a dictionary in this format (note that the second element in the tuple will be the key):

A_dict = { 1: {2:72, 4:96},
           2: {1:72, 4:80},
           3: {},
           4: {1:96, 2:80, 5:70},
           5: {4:70},
         }

Is there a way to convert A to A_dict?

I tried this:

A_dict = {b:{a:c} for a,b,c in A}

but I got an error:

ValueError: not enough values to unpack (expected 3, got 2)

Answer 1

You can just do:

A_dict = {k+1: {t[2]: t[0] for t in l} for k, l in enumerate(A)}

>>> A_dict
{
 1: {2: 72, 4: 96}, 
 2: {1: 72, 4: 80}, 
 3: {}, 
 4: {1: 96, 2: 80, 5: 70}, 
 5: {4: 70}
}

Answer 2

By iterating on the indices of the list, according to its length. And for each value building its own dictionary:

A_dict = {i + 1 : {v[2] : v[0] for v in A[i]} for i in range(len(A))}

will output:

{1: {2: 72, 4: 96},
 2: {1: 72, 4: 80},
 3: {},
 4: {1: 96, 2: 80, 5: 70},
 5: {4: 70}}

Actually your desired code is:

A_dict = {A[i][0][1] : {v[2] : v[0] for v in A[i]} for i in range(len(A)) if len(A[i]) > 0}

But that will 'skip' the third line, as there is no list, thus not able to determinate the actual key, according to your specification.