Is there a better way to write nested if statements in python? [closed]

Insert all the valid combinations to a dictionary of tuples, and if the combination is not there, return 0:

def convert_what(numeral_sys_1, numeral_sys_2):
    numeral_dict = {
        ("Hexadecimal", "Decimal"    ) : 1,
        ("Hexadecimal", "Binary"     ) : 2,
        ("Decimal",     "Hexadecimal") : 4, 
        ("Decimal",     "Binary"     ) : 6,
        ("Binary",      "Hexadecimal") : 5,
        ("Binary",      "Decimal"    ) : 3
    }
    return numeral_dict.get((numeral_sys_1, numeral_sys_2), 0)

If you are planning to use the function in a loop, it may be a better idea to define the dictionary outside the function, so it wouldn’t be recreated on every call to the function.