Getting error when called through instance method

[aankrose]

Hello Python Experts

Below code works without any issues when i called it though class method BUT when i called it through instance method , it is not working , may i please know why?

Working Code

class Pizza:
    def __init__(self, size):
        self.size = size
    def get_size(self):
        return "Size={}".format(self.size)

print(Pizza.get_size(Pizza(4555))

Output:
==> Size=4555

Error Code

class Pizza:
    def __init__(self, size):
        self.size = size
    def get_size(self, data):
        return "Size={}".format(self.size)

print(Pizza.get_size(4555))

Error:
aankrose@PS1:~/code$ python3 phase2.py
Traceback (most recent call last):
  File "phase2.py", line 7, in <module>
    print(Pizza.get_size(4555))
TypeError: get_size() missing 1 required positional argument: 'data'