如何使父 class object 指代子 class？

Question

Like in java or C# where we can create an object like

Account obj = new SavingsAccount();

where Account is the parent class and SavingsAccount is the child class

How do I do the same thing with python?

basically I'm trying to do is this https://repl.it/@MushfiqurRahma1/Polymorphic-Object

Answer 1

Python is dynamically typed: names refer to objects without any notion of type being involved. You just have

>>> class Account: pass
...
>>> class SavingsAccount(Account): pass
...
>>> obj = SavingsAccount()

Each object stores a reference to its own type

>>> type(obj)
<class '__main__.SavingsAccount'>

and each type has a referent to its method resolution order (MRO)

>>> type(obj).__mro__
(<class '__main__.SavingsAccount'>, <class '__main__.Account'>, <class 'object'>)

Instance attributes are not "compartmentalized" according to the class that "defines" them; each attribute simply exists on the instance itself, without reference to any particular class.

Methods exist solely in the classes themselves; when it comes time to call obj.foo() , the MRO is used to determine whose definition is used.

Answer 2

Python uses Duck typing, which means you shouldn't really care about the class in the Left side of the assignment. Just instantiate the Child class and you should already be able to use it's parent “interface” to do stuff like dynamic method calls.

Answer 3

Python is a loosely typed language. That means you don't have to specify your variable types. You could just do something like:

class Account():
    def deposit():
        pass
class SavingsAccount(Account):
    pass

obj = SavingsAccount()
obj.deposit(20)

EDIT : As chepner pointed out: Python is strongly typed, but also dynamically typed: type is associated with an object, not the name referring to an object.