How to implement command design pattern in python?
import abc class CalcCmdAbs(metaclass=abc.ABCMeta): def __init__(self, *args, **kwargs): self._args = args self._kwargs = kwargs @property @abc.abstractmethod def name(self): raise NotImplemented() def execute(self): raise NotImplemented() from .interface import CalcCmdAbs OPERATORS = list() def register_operator(cls): OPERATORS.append(cls) return cls @register_operator class AddCmd(CalcCmdAbs): name = "add" def __init__(self, a, b): super().__init__(a, b) self.a = a self.b = b def execute(self): return self.a + self.b @register_operator class SubtractCmd(CalcCmdAbs): name = "subtract" def __init__(self, a, b): super().__init__(a, b) self.a = a self.b = b def execute(self): return self.a - self.b class NoneCmd(CalcCmdAbs): name = "None Command" def execute(self): print("Invalid Command") from .commands import OPERATORS, NoneCmd def get_commands() -> dict: return dict([cmd.name, cmd] for cmd in OPERATORS) def parse_commands(commands: dict, operation: str, *args): command = commands.setdefault(operation, NoneCmd) return command(*args) import unittest from .utils import get_commands, parse_commands class TestCase(unittest.TestCase): def setUp(self) -> None: self.commands = get_commands() def test_addition(self): command = parse_commands(self.commands, "add", 1, 1) self.assertEqual(command.execute(), 2, "Addition fail") def test_subtraction(self): command = parse_commands(self.commands, "subtract", 1, 1) self.assertEqual(command.execute(), 0, "Subtraction fail")