How to override only one variable inside parent class's method?

Question

Let's suppose that Parent class is:

class Parent:

  def __init__(self, a):
    self.a = a

  def do_something(self):
    a = self.a
    b = self.a
    print('The a is ', a)
    print('The b is ', b)

I want to create a Child class that will redefine only b

Something like:

class Child(Parent):

  def do_something(self, custom_param):
    @some_exotic_decorator_or_something_else(b=custom_param)
    super().do_something()

And get output like:

obj = Child('the_a')
obj.do_something('the_b')

The a is the_a
The b is the_b

Of course original method has many lines and complicated logic to override whole method. Also that is one of common python libraries so I want to minimise intrusion inside method.

Here is any common way in python to do that?

To be more clear, the method what I want to override is _write_end_record

I want to redefine only centDirOffset . All other logic is working good. I may copy and paste whole method inside my code and change only one line, but it don't looking like a smart idea

Answer 1

A clean and easy way would be to make your parent class more general by adding a parameter to your method and assign a default value to it.

class Parent:

    def __init__(self, a):
        self.a = a

    def do_something(self, b=None):
        if b is None:
            b = self.a
        a = self.a
        print('The a is ', a)
        print('The b is ', b)

By doing this, you do not even need a child class.