Question

I’ve implemented a Finite state machine in python. This works but implementing a state needs to write unnecessary code.

class State:
    def __init__(self):
        <do something>

    def __call__():
       <do something different>

class ConcreteState(State):
    def __init__(self):
       super().__init__()

    def __call__():
        super().__call__()
       <do concrete state implementation>

Is it possible to make a decorator in order to implement a concrete state like the following example?

@StateDecorator
def concreteState():
   <do concrete state implementation>

Answer 1

It’s ugly, but since a decorator can return anything it’s OK for it to return a class instead of a function:

def StateDecorator(fn):
    class cls(State):
        def __call__(self):
            super().__call__()
            fn(self)
    return cls

@StateDecorator
def concreteState(self):
    print("cc", self)

concreteState
<class '__main__.cls'>

Be aware that this could confuse any static analysis tools you’re using.