how to get an index of an element of tuple or list which itself is an element of a list

Question

The codes:

 Cour_det = [("MA101","Calculus"),("PH101","Mechanics"),("HU101","English")];
 Stu_det = [("UGM2018001","Rohit Grewal"),("UGP2018132","Neha Talwar")];
 Grades = [("UGM2018001", "MA101", "AB"),("UGP2018132", "PH101", "B"),
 ("UGM2018001", "PH101", "B")];
 Cour_det = sorted(Cour_det, key = lambda x : x[0]);
 Stu_det = sorted(Stu_det, key = lambda x : x[0]);
 Grades = sorted(Grades, key = lambda x : x[1]);
 Grades = sorted(Grades, key =lambda x : x[0]);
 B={}
 #code by which i tried to add grade to nested list
 for i in range(len(Stu_det)):
     for j in range(len(Cour_det)):
         B[Stu_det[i][0]][Cour_det[j][0]]=(Cour_det[j][1],Grades[][])
         #here i am stuck on how to access grade of the course that i am adding
 #it should look like this
 B={"UGM2018001":{"MA101":("Calculus","AB'),"PH101":("Mechanics","B")}}
 #above list for roll no UGM2018001,similarly other roll no.s as keys and
 #course code can be keys of nested list for those roll no.s

In this code i want to make a nested dictionary in which the outer keys will be the roll no as what first element of every tuple of List Stu_det is( like UGM2018001) and then the nested keys will be the course code( like MA101 ) and then the element of each nested key will be a tuple or list which will have two elements, first element will be the course name( like Calculus ) and second element i want the grade mentioned ( like AB ) but accessing the grade is becoming problem ,how to access it or to get its index. I am unable to get Grade of subject after making roll no. and course code key.

Answer 1

Here's a way of doing it using defaultdict module.

# load library
from collections import defaultdict

# convert to dictionary as this will help in mapping course names
Cour_det = dict(Cour_det)
Stu_det = dict(Stu_det)


# create a dictionary for grades
grades_dict = defaultdict(list)
for x in Grades:
    grades_dict[x[0]].append(x[1:])

# create a new dict to save output
new_dict = defaultdict(dict)

# loop through previous dictionary and replace course codes with names
for k,v in grades_dict.items():

    for val in v:
        temp = list(val)
        temp[0] = Cour_det[temp[0]]
        new_dict[k].update({val[0]: tuple(temp)})

# print output        
print(new_dict)
defaultdict(dict,
        {'UGM2018001': {'MA101': ('Calculus', 'AB'),
          'PH101': ('Mechanics', 'B')},
         'UGP2018132': {'PH101': ('Mechanics', 'B')}})