unbound method must be called with instance as first argument - python

Question

I keep on receiving the error: TypeError: unbound method get_num_students() must be called with Student instance as first argument (got nothing instead)

Her

Answer 1

It seems like you wanted to define grad_early, get_num_students and get_grad_2013 as class methods, but you declared them as instance methods instead.

An instance method is a method that, well, belongs to an instance of the class.

An example would be

class Student(object):
    # ...

    def print_name(self):  # This is an instance method
        print "executing instance method"

    @classmethod
    def num_of_students(cls)
        print "executing class method"

The difference is that an instance method will work on s = Student() s.print_name()

And a class method will work on the class itself Student.