append key values to dictionary from list

Question

I am trying to create a dictionary from a parallel list, I am stuck because using zip and setdefault method doesn' allow more than 2 arguments. Can anybody assist

mainList=["A","B"]
mainListValue1=[1,22,3]
mainListValue2=["v1","v2"]
mainListValue3=["v4","v5"]
final_dict = {}
for mainList, mainListValue1, mainListValue2 in zip(mainList, mainListValue1, mainListValue2):
    final_dict.setdefault(mainList, list()).append(mainListValue1)


print(final_dict)

Looking for following output

{'A': 
     1,
     'v1',
     'v4' 
'B': 
     22,
     'v2',
     'v5'
     }

Answer 1

First, note that your desired output is syntactically incorrect since the values of the dictionary are not coherently defined, ie you need the values to be packaged in something like a list. Otherwise, the Python interpreter would mistakenly believe that, for example, the 'v1' element is not a value for 'A' , but a start of a new key value.

With that in mind, here is a simple approach of looping through the lists to group elements into a value for a dictionary.

result = {}

for i, key in enumerate(mainList):
    value = []
    for lst in [mainListValue1, mainListValue2, mainListValue3]:
        value.append(lst[i])
    result[key] = value

print(result)

The result is the following output:

{'A': [1, 'v1', 'v4'], 'B': [22, 'v2', 'v5']}

I'd be happy to answer any additional questions you might have.

Answer 2

If the lists are parallel like that, you don't need setdefault() , just use zip() in conjunction with a dictionary comprehension like this:

#!/usr/bin/env python3
# https://stackoverflow.com/questions/60085285/append-key-values-to-dictionary-from-list

mainList = ["A","B"]
mainListValue1 = [1, 22, 3]
mainListValue2 = ["v1", "v2"]
mainListValue3 = ["v4", "v5"]

final_dict = {key: tuple(values) for key, *values
                in zip(mainList, mainListValue1, mainListValue2, mainListValue3)}

print(final_dict)  # -> {'A': (1, 'v1', 'v4'), 'B': (22, 'v2', 'v5')}

Note that the 3 in mainListValue1 gets ignored because the lists really aren't parallel.