Using __init__ method to call class main functionality

I needed to encapsulate functions related to single responsibility of parsing and emiting messages to API endpoint so I have created class Emitter.

class Emitter:
    def __init__(self, message: str) -> None:
        self.parsed = self.parse_message(message)
        self.emit_message(self.parsed)

    @staticmethod
    def parse_message(msg: str) -> str:
        ...  # parsing code

    @staticmethod
    def emit_message(msg: str) -> None:
        ...  # emitting code

In order to emit a message I call a short-lived instance of that class with message passed as argument to __init__.

Emitter("my message to send")

__init__ itself directly runs all necessary methods to parse and emit message. Is it correct to use __init__ to directly run the main responsibility of a class? Or should I use different solution like creating function that first instantiates the class and then calls all the necessary methods?

Answer

It looks like you’re attempting to do the following at once:

1. initialize a class Emitter with an attribute message
2. parse the message
3. emit the message

IMO, a class entity is a good design choice since it allows granular control flow. Given that each step from above is discrete, I’d recommend executing them as such:

# Instantiate (will automatically parse)
e = Emitter('my message')

# Send the message
e.send_message()

You will need to redesign your class to the following:

class Emitter:
    def __init__(self, message: str) -> None:
        self.message = message
        self.parsed = self.parse_message(message)

    @staticmethod
    def parse_message(msg: str) -> str:
        ...  # parsing code

    # This should be an instance method
    def emit_message(msg: str) -> None:
        ...  # emitting code

Also, your parse_message() method could be converted to a validation method, but that’s another subject.