switch_0.py

# switch_0.py
# Runs actions/values as they are found


class FirstMatchFound(Exception):
    pass


class InvalidResultTypeError(Exception):
    pass


class UnexhaustivePatternsError(Exception):
    pass


class Action:
    def __init__(self, func, *args, **kwargs):
        self.func = func
        self.args = args
        self.kwargs = kwargs

    def __call__(self):
        return self.func(*self.args, **self.kwargs)


class Value:
    def __init__(self, value):
        self.value = value

    def __call__(self):
        return self.value


class Switch:
    def __init__(self, expected, *, default=None):
        self.against = None
        self.default = default
        self.expected = expected
        self.result = None

    def __call__(self, against):
        self.against = against
        return self

    def __rshift__(self, value_or_action):

        if not isinstance(value_or_action, (Action, Value)):
            raise InvalidResultTypeError("Expecting either 'Action' or 'Value'")

        if self.expected == self.against:
            self.result = value_or_action()
            raise FirstMatchFound(f"Match found {self.result}")

    def __enter__(self):
        return self

    def __exit__(self, exception, value, traceback):
        if exception is FirstMatchFound:
            return True

        elif exception is InvalidResultTypeError:
            return True

        elif self.default is None:
            raise UnexhaustivePatternsError

        self.result = self.default()

        return False

with Switch("foo") as Case:
    Case("foo") >> Action(print, "Hello, World")
    Case("bar") >> Value("Hello, Bar")

switch_1.py

# switch_1.py
# Runs actions/values on exit


class FirstMatchFound(Exception):
    pass


class InvalidResultTypeError(Exception):
    pass


class UnexhaustivePatternsError(Exception):
    pass


class Action:
    def __init__(self, func, *args, **kwargs):
        self.func = func
        self.args = args
        self.kwargs = kwargs

    def __call__(self):
        return self.func(*self.args, **self.kwargs)


class Value:
    def __init__(self, value):
        self.value = value

    def __call__(self):
        return self.value


class Switch:
    def __init__(self, expected, *, default=None):
        self.expected = expected
        self.default = default

        self.mapping = {}
        self.current = None
        self.result = None

    def __call__(self, current):
        self.current = current
        return self

    def __rshift__(self, value_or_action):
        if not isinstance(value_or_action, (Action, Value)):
            raise InvalidResultTypeError("Expecting either 'Action' or 'Value'")
        self.mapping[self.current] = value_or_action

    def __enter__(self):
        return self

    def __exit__(self, exception, value, traceback):
        if exception is InvalidResultTypeError:
            return True

        if self.expected in self.mapping:
            self.result = self.mapping[self.expected]()
            return False

        elif self.default is None:
            raise UnexhaustivePatternsError

        else:
            self.result = self.default()
            return False


with Switch("foo") as Case:
    Case("foo") >> Action(print, "Foo")
    Case("bar") >> Action(print, "Bar")