TypeError: super(type, obj): obj must be an instance or subtype of type 에러 이유 및 해결방법

1. Error Code

Class A:
	def func(x: int):
    	return x + 1

Class B(A):
	def use_func():
    	a = [super().func(i) for i in range(3)]
        print(a)

the original code is different and has been modified since posting it online could cause code leaks of the company I am working for.

Yet, I believe this code explains the prob perfect.

I got an error in this line: 

a = [super().func(i) for i in range(3)]

2. The cuase, 에러 이유

List comprehension has its own scope in Python 3 while Python 2 does not. That is the key to resolve this error.

To get deeper, In Python 2, super() requires users to put 2 arguments, type and object. So, the code used to be like this:

// This code is in B class
// B is A's child class which self refers to
a = [super(B, self).func(i) for i in range(3)]

In Python 3, though we don't have to clarify the arguments anymore, super() still gets arguments internally. However, List comprehension doesn't have self in it. That code would've worked if i had used Python 2.

 

3. Fix the error

To fix this problem, code changes are needed. Below is the changed code.

Class A:
	def func(x: int):
    	return x + 1

Class B(A):
	def use_func():
   		a = []
    	for i in range(3):
        	a.append(super().func(i))
            
        print(a)