Calculating student and class averages

Question

I am currently going through Codecademy's Python course (I don't come from a coding background but I'm thoroughly enjoying it) and I got to the end of one of the sections and thought, "Well it worked, but that seemed wildly inefficient." I tried shortening unnecessary parts and came up with this:

lloyd = {
 "name": "Lloyd",
 "homework": [90.0, 97.0, 75.0, 92.0],
 "quizzes": [88.0, 40.0, 94.0],
 "tests": [75.0, 90.0]
}
alice = {
 "name": "Alice",
 "homework": [100.0, 92.0, 98.0, 100.0],
 "quizzes": [82.0, 83.0, 91.0],
 "tests": [89.0, 97.0]
}
tyler = {
 "name": "Tyler",
 "homework": [0.0, 87.0, 75.0, 22.0],
 "quizzes": [0.0, 75.0, 78.0],
 "tests": [100.0, 100.0]
}
classlist = [lloyd, alice, tyler]
# Add your function below!
def get_average(student):
 average_homework = sum(student["homework"]) / len(student["homework"])
 average_quizzes = sum(student["quizzes"]) / len(student["quizzes"])
 average_tests = sum(student["tests"]) / len(student["tests"])
 average_total = average_homework * 0.1 + average_quizzes * 0.3 + average_tests * 0.6
 return average_total
def get_letter_grade(score):
 if score >= 90:
 return "A"
 if score < 90 and score >= 80:
 return "B"
 if score < 80 and score >= 70:
 return "C"
 if score < 70 and score >= 60:
 return "D"
 else:
 return "F"
def get_class_average(classlist):
 a = []
 for student in classlist:
 a.append(get_average(student))
 return sum(a) / len(a)
get_class_average(classlist)

Now this bit works, but I was wondering if there are more places I could trim the code down without losing the functionality (I'm guessing there is in the get_average function but the things I tried came back as errors because of the "name" field in the dictionary). Codecademy seems good for learning the fundamentals, but I wanted to get some insight into the "best" way to do things. Should I not worry about reworking functional code to be more efficient at first and just learn the fundamentals, or should I keep trying to make the "best" code as I learn?

• SylvainD: Can you add information about the problem you are trying to solve ?
• Aseem Bansal: @Josay Actually he isn't trying to solve any problem. This is the part of the python track on codecademy.com. One introducing to dictionary in Python.

Answer 1

In average_student, you're manually iterating over the keys in a dictionary, and you've hardcoded the weights of the various parts. What if you want to add a "presentation" component to the grade? You've got a lot of places to touch.

Consider exporting the hardcoded information into its own dictionary, and iterating over the keys in that dictionary:

weights = {
 "homework": 0.1,
 "quizzes": 0.3,
 "tests": 0.6
}
def get_average(student):
 return sum(average(student[section]) * weights[section] for section in weights)
def average(x):
 return sum(x)/len(x)

In terms of learning Python, I'd definitely agree with your instinct -- you should keep trying to make your code as clean as possible even while completing exercises. When you're learning fundamentals, it's that much more important to understand good structure.

• Aseem Bansal: Is this the get_average function? I tried but couldn't run it.
• llb: Oops! I had a syntax brainfart. Fixed it.
• Raynman37: @llb Thanks for this input too! get_average was the section I didn't like when I got done with it either. Exactly like you said that whole section was basically hardcoded in there. I'll definitely be playing with this today as well!

Answer 2

Defining an average function (based on this), you could have things slightly clearer :

def average_list(l)
 return sum(l) / float(len(l))
def average_student(student):
 average_homework = average_list(student["homework"])
 average_quizzes = average_list(student["quizzes"])
 average_tests = average_list(student["tests"])
 average_total = average_homework * 0.1 + average_quizzes * 0.3 + average_tests * 0.6
 return average_total
def class_average(students):
 return average_list([average_student(s) for s in students])

• Aseem Bansal: You are not using the description in the link that you provided. You just added a function call which can be used in the other function as well.
• Aseem Bansal: Actually I was talking about using reduce and lambda. Anyways you don't need to use float in the average_list function either. All the values are float already so sum would also be. Implicit conversion so explicit isn't needed.
• Raynman37: @Josay Are we supposed to use class in the class_average section because it's already a built in Python term (I don't know what you'd call it officially)?
• SylvainD: Raynman37 : As per docs.python.org/release/2.5.2/ref/keywords.html this is a valid comment. It completely went out of my mind but I'm going to change this.

Answer 3

• In the function get_letter_grade you were checking more conditions then necessary. Try to follow the logical difference between your function and my code. It is simple math which I used to optimize it. Also structuring it as an if-elif-...-else is better for readability.
• In get_average and get_class_average I use a thing called list comprehension. A simple google search will tell you what it is and why it is better. Google it in python tutorials if you have problem.

Edited Functions

def average(values):
 return sum(values) / len(values)
def get_average(student):
 keys = ['homework', 'quizzes', 'tests']
 factors = [0.1, 0.3, 0.6]
 return sum([ average(student[key]) * factor for key, factor in zip(keys, factors)])
def get_letter_grade(score):
 if score >= 90:
 return "A"
 elif score >= 80:
 return "B"
 elif score >= 70:
 return "C"
 elif score >= 60:
 return "D"
 else:
 return "F"
def get_class_average(classlist):
 return average([get_average(student) for student in classlist])
get_class_average(classlist)

• Raynman37: I would vote you up, but I don't have 15 reputation. This is exactly what I was meaning. It works to Codeacademy standards, but could easily be refined. Thanks for the list comprehension pointer as well!
• Aseem Bansal: @Raynman37 Edited the answer a bit more. Try to figure out how the return statement of get_average works. Yeah you cannot vote up but you can accept an answer.
• Bakuriu: Actually you don't need a list-comprehension. A generator expression works too, and avoids the creation of the intermediate list.
• Aseem Bansal: @Bakuriu Yeah that would have been better. There are two reasons I didn't do that. FIrstly, the OP is a beginner and I don't think introducing generators to a beginner would be a good idea. Secondly, I am not much experienced in Python either so my explanation might not have been the best. If he is interested here is a link to a question on stackoverflow
• fjarri: I would have used zip in get_average(): return sum([average(student[key]) * factor for key, factor in zip(keys, factors)]).