Python beginner OOP functions

Question

Can you help me to solve the problem, why am I not able to call my functions? I try to calculate the average mark of all student objects created but it somehow doesnt work.

class Student:
 anz = 0
 def __init__(self, vorname, nachname, studetnId, averageMark):
 self.vorname = vorname
 self.nachname = nachname
 self.studentId = studetnId
 self.averageMark = averageMark
 Student.anz += 1
 def totalAverageMark(self, input):
 summe = 0
 for s in input:
 summe += self.averageMark
 return (summe / Student.anz)
 def getName(self, arr):
 for s in arr:
 return self.nachname
students = [Student("Maxine", "Muster", 2, 1.0), Student("Bert", "Beispiel", 1, 2.0)]
print(students.getName())
print(students.totalAverageMark())

It says: AttributeError: 'list' object has no attribute 'totalAverageMark'

• jarmod: Somehow? How exactly? Always include error messages and explain how your code is failing so we don't have to guess or work it out. Do you know how to use lists (such as students) in Python?
• juanpa.arrivillaga: students is a list. As the error tells you, list objects do not have those methods
• Ulrich Eckhardt: There is one conceptional error as well: You can ask a Student for their name (getName()), but asking one about the total average mark (totalAverageMark()) you can't expect them to return any info that includes other students. BTW: What is the meaning of the parameter to getName()? It doesn't make sense. You'd see that yourself if you made a human language description of what each method does, including the paramers.
• shivankgtm: would like to suggest not to use keywords like input as a parameter name in def totalAverageMark(self, input):.
• Martin Müller: @Ulrich Eckhardt Ok, got that! So that is why I need to create a new class or just some code outside the functions right?

Answer 1

Student define attributes of a single student only single. to get the collective result for example avg mark of all student, you need to create a class (that bind all students say) that defines the attribute of the class ie there students.

below is a simple implementation what you are trying to do using OOPs

class Student:
 def __init__(self, vorname, nachname, studetnId, averageMark):
 self.vorname = vorname
 self.nachname = nachname
 self.studentId = studetnId
 self.averageMark = averageMark
class Students:
 def __init__(self, students_list: list):
 self.students = students_list
 def avg_marks(self):
 total_students = len(self.students)
 marks = sum(student.averageMark for student in self.students)
 return marks/total_students
students = [Student("Maxine", "Muster", 2, 1.0), Student("Bert", "Beispiel", 1, 2.0)]
student_data = Students(students)
print(student_data.avg_marks())

• Martin Müller: Wow, thanks a lot. I believe I can figure out what you mean.

Answer 2

students is a list of your students. List has not functions getName and totalAverageMark. You can use them only with object of Student class.

Simplest way to get total average mark of students:

class Student:
 anz = 0
 def __init__(self, vorname, nachname, studetnId, averageMark):
 self.vorname = vorname
 self.nachname = nachname
 self.studentId = studetnId
 self.averageMark = averageMark
 Student.anz += 1
students = [Student("Maxine", "Muster", 2, 1.0), Student("Bert", "Beispiel", 1, 2.0)]
sum = 0
for s in students:
 sum += s.averageMark
print(f"Total average mark is {sum / len(students)}")

• jarmod: I think it would help to expand your answer to show how to call these methods against one or more students.
• Martin Müller: Well exactly, I understand what @Ratery means. But how am I able to iterate through the list, and therefore get the total Average mark?
• juanpa.arrivillaga: @MartinMüller what do you mean? Are you asking how to iterate over a list? This really has nothing to do with your stated question.
• Ratery: @MartinMüller I have edited my answer. You don't need class methods to do it.
• Martin Müller: So it should also be possible to write that in a method, right?

Answer 3

You are trying to call the methods getName() and totalAverageMark() directly on the students list object instead of accessing each individual Student objects within the list.

Iterate over each Student object in the students list and call the methods on each object:

class Student:
 anz = 0
 def __init__(self, vorname, nachname, studentId, averageMark):
 self.vorname = vorname
 self.nachname = nachname
 self.studentId = studentId
 self.averageMark = averageMark
 Student.anz += 1
 @staticmethod
 def totalAverageMark(students):
 summe = 0
 for student in students:
 summe += student.averageMark
 return summe / len(students)
 def getName(self):
 return self.nachname
students = [Student("Maxine", "Muster", 2, 1.0), Student("Bert", "Beispiel", 1, 2.0)]
average_mark = Student.totalAverageMark(students)
print(f"Average Mark: {average_mark}")
for student in students:
 name = student.getName()
 print(f"Student Name: {name}")

Answer 4

To iterate through the list and print out the result for each student you can use the following:

for student in students:
 print(student.getName())
 print(student.totalAverageMark())

Or to access an individual student

students[0].getName()

• Ulrich Eckhardt: Yes, but no: This won't run. Also, it won't give the average mark of all students.