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

Differences in In python 2 and 3 version:

If you already have a default method in a class with same name and you re-declare as a same name it will appear as unbound-method call of that class instance when you wanted to instantiated it.

If you wanted class methods, but you declared them as instance methods instead.

An instance method is a method that is used when to create an instance of the class.

An example would be

   def user_group(self):   #This is an instance method
        return "instance method returning group"

Class label method:

   @classmethod
   def user_group(groups):   #This is an class-label method
        return "class method returning group"

In python 2 and 3 version differ the class @classmethod to write in python 3 it automatically get that as a class-label method and don't need to write @classmethod I think this might help you.

Answer 2

When you define an instance method, put a self as the method's first argument, and when you use it, add self. in front of your instance variable.

Like:

def get_num_students(self):
    print "There are %s students in this school." % (self.num_students)

Answer 3

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.