Python字典中的平均值

Question

I am trying to find the average of maths score for the class but I am not sure how to do this within a dictionary. How do I use a simple method of adding each score then dividing this by the number of students (num_students)?

login="teacher"
password="school"

usrnm=input("Please enter your username: ")
pw=input("Please enter your password: ")
if (usrnm==login) and (pw==password):
   print("==Welcome to the Mathematics Score Entry Program==")
   num_students = int(input("Please enter number of students:"))
   print ("you entered ",num_students," students")
   student_info = {}
   student_data = ['Maths Score: ']
   for i in range(0,num_students):
      student_name = input("Name :")
      student_info[student_name] = {}
      for entry in student_data:
        student_info[student_name][entry] = int(input(entry)) 
   print (student_info)
else:
  print("No way, Jose!")

Answer 1

Calculating the average can be done using the sum function as follows:

average = sum(d['Maths Score: '] for d in student_info.values()) / len(student_info)

Note that currently your code can only have students with unique names. Two students with the same name will override each other.

Answer 2

python dictionaries have a .values() method which returns a list of the values in a dictionary which you can use, eg:

sum(d.values()) / float(len(d))

d.values() give the list of marks for your students, sum(..) gives the total of all the marks, which I divide by len(d) which is the integer length of the dictionary (ie the number of marks) obviously average is total of marks / number of marks.

you need the float because python 2 will return an integer otherwise (python 3 gives floats when appropriate)

Answer 3

If you're using Python 3.4+, then you can use statistics.mean :

from statistics import mean
avg_score = mean(d.values())