Loop example | Python Fiddle

students = [] 	#this assigns the first student list, and is empty 
grades = []		#this assigns the first grades list, and is empty
grades2D = []	#this assigns the first and the grades and names list, and is empty

while True:
    print("Option1: Enter a score")							#When the program is first run it displays the three lines of instructions:
    print("Option2: Display the grades")
    print("Option3: Exit")									#the "option =" creates a changeable variable because it is followed by an "input" command
    option = input("Enter option here: ").strip().lower()	#using .strip() removes any blank spaces either before or after the input, and .lower() changes the input to all lowercase
    if option == "1":										#the == means that if option entered above is equal to 1 then this if statement runs
  	#if "1"  in option:										#this may be a more usuful command as if the user doesnt just enter 1 then it will still work.
        name = input("Enter the students name: ")			#"name =" creates an object called name, and then makes it equal to whatever is typed
        score = int(input("Please enter the score between 0 & 100 you wish to convert: "))
        
        if score <0:										#if the score is lower than 0 then this piece of code runs
            print("You can't have a negative score")		#and displays this print
        elif score <=30:									#otherwiise it runs this elif code
            students.append(name)							#this adds the name defined earlier to the "students" list
            grades.append("U")								#this adds the grade to the end of the "grades" list            grades2D.append([name, "U"])
            grades2D.append([name, "U"])					#this adds both the name followed by the grade to a seperate list
        elif score <=40:									#if the above elif is not run then this one will be run instead
            students.append(name)
            grades.append("E")
            grades2D.append([name, "E"])
        elif score <=50:
            students.append(name)
            grades.append("D")
            grades2D.append([name, "D"])
        elif score <=60:
            students.append(name)
            grades.append("C")
            grades2D.append([name, "C"])
        elif score <=70:
            students.append(name)
            grades.append("B")
            grades2D.append([name, "B"])
        elif score <=100:
            students.append(name)
            grades.append("A")
            grades2D.append([name, "A"])					
        elif score >100:									#this section is here to make sure that data is entered correctly, and so no values over 100 can be entered 
            print("You can't have a score greater than 100")
        else:												#this else command is used to cover any other possibilities
            print("Please enter a number between 0 and 100")
            
    elif option == "2":										#this checks to see if option 2 is chosen
    #if "2"  in option:										#this may be a more usuful command as if the user doesnt just enter 1 then it will still work.    
        counter = 0											#this creates a counter variable, and sets it equal to 0
        for student in students:							#this says for all the individual student added to the students list, and repeats the code until they're all done
            print(student + " achieved a " + grades[counter] + " grade") #print their name, the text, then their grade using the counter
            counter +=1										#then add one relative to the counter
    elif option == "3":				
    #if "3"  in option:										#this may be a more usuful command as if the user doesnt just enter 1 then it will still work.    
        break												#This section of code breaks the script at this point, which closes the program.
    elif option == "4":										#this is a hidden option and is another way of displaying their grades.
    #if "4"  in option:										#this may be a more usuful command as if the user doesnt just enter 1 then it will still work.
        for students in grades2D:							#this says repeat for all the students in the grades2D list
            1
            print(student[0] + " achieved a " + student[1] + " grade")	# this will print the students name then their grade through just one list
	else:													#otherwsie it will print the below message.
   	    print("Please enter a valid choice of 1,2 or 3")

Python Fiddle

Python Cloud IDE