simplifying a stack of elifs

[Gribouillis]

every command involves accessing and modifying local variables

Make these variables members of a class instance and dispatch things on instance methods.

class CommandHandler:
    dispatch = {
        'spam': 'on_spam',
        'eggs': 'on_eggs',
    }

    def __init__(self, ...):
        self.foo = ...
        self.bar = ...

    def __call__(self, msg):
        getattr(self, self.dispatch[msg[0]])()

    def on_spam(self):
        self.foo = 3452

    def on_eggs(self):
        self.foo = 1233

Instance variables are the normal way to share data between several functions.

You can also use new classes to manage individual commands

class Command:
    def __init__(self, handler):
        self.handler = handler

class Spam(Command):
    def run(self):
        self.handler.foo = 1023

class Eggs(Command):
    def run(self):
        self.handler.foo = 1048

class CommandHandler:
    dispatch = {
        'spam': Spam,
        'eggs': Eggs,
    }

    def __init__(self, ...):
        self.foo = ...
        self.bar = ...

    def __call__(self, msg):
        self.dispatch[msg[0]](self).run()