How to call a function from another class in python

Question

class A:
  def add_f(self,a,b):
    return a+b

class B:
  def sum_f(self,a,b,c):
    return A.add_f(a,b) + c

B1= B()    
print B1.sum_f(1,2,3)


Traceback (most recent call last):
File "C:/Users/wxu/Documents/test.py", line 10, in <module>
print B1.sum_f(1,2,3)
File "C:/Users/wxu/Documents/test.py", line 7, in sum_f
return A.add_f(a,b) + c
TypeError: unbound method add_f() must be called with A instance as first argument (got int instance instead)

When I don't have the self for sum_f(self,a,b,c), it gave me this error:

Traceback (most recent call last):
File "C:/Users/wxu/Documents/test.py", line 10, in <module>
print test1.sum_f(1,2,3)
TypeError: sum_f() takes exactly 3 arguments (4 given)

Why is that? And how to call function add_f from class A in class B? Thank you for your help.

Answer 1

There was a few things.

1. When you define class methods, they must have self as the first parameter.
2. The part where you had an error is where you tried to call B as a variable. B is a class, and you must call it like any other class. This also applies when you are calling A() in class B.

Revised code:

class A:
    def add_f(self, a, b):
        return a + b

class B:
    def sum_f(self, a, b, c):
        return A().add_f(a, b) + c

print B().sum_f(1, 2, 3)

Update: Thanks for taking my advice but you're still missing something. In class B you call a method from class A, but you need parentheses for that too! In class B, call class A as such:

A().add_f(a, b)

Answer 2

Simple fixes, you just need to open and close the brackets on your class declarations, so class B becomes class B() (Same thing applied to class A). Also, you need to add some kind of variable such as self as the first argument of each method declared within a class. You never need to pass anything as this first argument to fill self, as python will do it for you.

As for your A.add_f issue, you just need to do as you did with B, and instantiate it an A object to something like A1, and then call the method of A1.