计算Python 3中列表的平均值

Question

I am currently trying to calculate the average of a list created by a method in a class. Firstly all information is passed to a Class that records/returns the data passed through from the main function. The issue is what do I pass in from the main function to firstly retrieve the self._marks list and then manipulate it in order for the average to be returned. Also am I using the correct code for the calculateAverageMark section? Thanks in advance

Here is the code:

class Student :
    def __init__(self, id):
        self._studentId = id
        self._marks = []
    ##
    # Converts the student to a string .
    # @return The string representation .
    #

    # Sets the student's ID.
    # @param newId is the student's new ID.
    #
    def setStudentId(self, id):
        self._studentId = id

    ##
    # Gets the student's ID.
    # @return the student's ID
    #
    def getStudentId(self, newId):
        return self._newId

    ##
    # Appends a mark to the marks list
    #
    def addMark(self, mark):
        self._marks.append(mark)

    def __repr__(self) :
        # Build a string starting with the student ID
        # followed by the details of each mark .
        s = "Student ID :" + self._studentId + " "
        if len(self._marks) == 0 :
            s += " <none \n>"
        else :
            for mark in self._marks :
                s += " Course Module: " + mark.getModule() + " Raw Mark: " + str(mark.getRawMark())

        return s

    ##
    # Method to calculate the students average mark
    #
    def calculateAverageMark(self):
        totalMarks = 0
        count = 0
        for mark in self._marks :
            if mark == 0 :
                count = count
            else :
                count = count + 1

            totalMarks = totalMarks + mark
            average = totalMarks / count

        return average

Answer 1

Your current code is incorrect because you divide by count in every iteration (and before count is actually the number of marks). Calculating the average is very easy with a list of values:

def calculateAverageMark(self):
    if self._marks: # avoid error on empty list
        return sum(self._marks) / float(len(self._marks))

You don't need to pass anything in; all instance attributes are available via self . Unless you have specifically been told to exclude zero scores from the average, you should count them.