https://github.com/ethereum/trinity/pull/175 https://github.com/ethereum/trinity/pull/193

command-class-factory.py

#!/usr/bin/env python

import logging

from pprint import pprint as pp

from typing import (
    Dict,
    List,
    Tuple,
    Type,
)

class Command:
    _cmd_id = None
    _cmd_id_offset = None
    _snappy_support = None

    @property
    def cmd_id(cls):
        return cls._cmd_id_offset + cls._cmd_id


class Hello(Command):
    _cmd_id = 0
class Disconnect(Command):
    _cmd_id = 1
class Ping(Command):
    _cmd_id = 2
class Pong(Command):
    _cmd_id = 3


command_classes: Dict[Tuple, Type[Command]] = {}
def init_command_class(cmd_class, cmd_id_offset, snappy_support):
    id = (cmd_class, cmd_id_offset, snappy_support)
    print('XXXXX', id)

    # use existing if available
    if id in command_classes.keys():
        print('XXXXX IN COMMAND CLASS CACHE')
        return command_classes[id]

    class _cmd_class(cmd_class):
        _cmd_id_offset = cmd_id_offset
        _snappy_support = snappy_support

        def __repr__(self):
            return f'{id}'
        # def __type__(self):
        #     return cmd_class

    c = _cmd_class()
    command_classes[id] = c
    return c


class Protocol:
    name: str = None
    version: int = None
    _commands: List[Type[Command]] = []

    _logger: logging.Logger = None

    def __init__(self, cmd_id_offset: int, snappy_support: bool) -> None:
        self._cmd_id_offset = cmd_id_offset
        self._snappy_support = snappy_support
        self._update_protocol_commands()
        return

    @property
    def logger(self) -> logging.Logger:
        if self._logger is None:
            self._logger = logging.getLogger(f'{type(self).__name__}')
        return self._logger

    def _update_protocol_commands(self) -> None:
        self.logger.debug('updating commands for %r', self)

        self.commands = [init_command_class(cmd_class, self._cmd_id_offset, self._snappy_support)
                         for cmd_class in self._commands]

        pp('commands:')
        pp(self.commands)

        self.cmd_by_type = {type(cmd): cmd for cmd in self.commands}

        pp('cmd_by_type:')
        pp(self.cmd_by_type)

        self.cmd_by_id = {cmd.cmd_id: cmd for cmd in self.commands}

        pp('cmd_by_id:')
        pp(self.cmd_by_id)

        return

    def supports_command(self, cmd_type: Type[Command]) -> bool:
        return cmd_type in self._commands


class P2PProtocol(Protocol):
    name = 'p2p'
    version = 5
    _commands = Protocol._commands + [Hello, Ping, Pong, Disconnect]

    def __init__(self, cmd_id_offset: int = 0, snappy_support: bool = False) -> None:
        super().__init__(cmd_id_offset, snappy_support)
        return


if __name__ == '__main__':
    logging.basicConfig(level=logging.DEBUG)
    logger = logging.getLogger('main')

    p0 = Protocol(0, False)
    protocols = [
        P2PProtocol(16, False),
        P2PProtocol(16, False),
        P2PProtocol(16, True),
    ]

    logger.info('='*72)

    logger.info('base class instance: %r', p0)
    logger.info('p2p class instances: %r', protocols)

    logger.info('command classes: %r', command_classes)
    logger.info('command count across all protocol instances: %s', len(command_classes))

    for protocol in [p0] + protocols:
        logger.info('%s supports Hello: %s', protocol, protocol.supports_command(Hello))
        for command in protocol.commands:
            logger.info('%r %s %s', command, command.cmd_id, command._snappy_support)

ZZ_out.py

DEBUG:Protocol:updating commands for <__main__.Protocol object at 0x7f0647032dd8>
'commands:'
[]
'cmd_by_type:'
{}
'cmd_by_id:'
{}
DEBUG:P2PProtocol:updating commands for <__main__.P2PProtocol object at 0x7f0647032e48>
XXXXX (<class '__main__.Hello'>, 16, False)
XXXXX (<class '__main__.Ping'>, 16, False)
XXXXX (<class '__main__.Pong'>, 16, False)
XXXXX (<class '__main__.Disconnect'>, 16, False)
'commands:'
[(<class '__main__.Hello'>, 16, False),
 (<class '__main__.Ping'>, 16, False),
 (<class '__main__.Pong'>, 16, False),
 (<class '__main__.Disconnect'>, 16, False)]
'cmd_by_type:'
{<class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Hello'>, 16, False),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Ping'>, 16, False),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Pong'>, 16, False),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Disconnect'>, 16, False)}
'cmd_by_id:'
{16: (<class '__main__.Hello'>, 16, False),
 17: (<class '__main__.Disconnect'>, 16, False),
 18: (<class '__main__.Ping'>, 16, False),
 19: (<class '__main__.Pong'>, 16, False)}
DEBUG:P2PProtocol:updating commands for <__main__.P2PProtocol object at 0x7f0647032e80>
XXXXX (<class '__main__.Hello'>, 16, False)
XXXXX IN COMMAND CLASS CACHE
XXXXX (<class '__main__.Ping'>, 16, False)
XXXXX IN COMMAND CLASS CACHE
XXXXX (<class '__main__.Pong'>, 16, False)
XXXXX IN COMMAND CLASS CACHE
XXXXX (<class '__main__.Disconnect'>, 16, False)
XXXXX IN COMMAND CLASS CACHE
'commands:'
[(<class '__main__.Hello'>, 16, False),
 (<class '__main__.Ping'>, 16, False),
 (<class '__main__.Pong'>, 16, False),
 (<class '__main__.Disconnect'>, 16, False)]
'cmd_by_type:'
{<class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Hello'>, 16, False),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Ping'>, 16, False),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Pong'>, 16, False),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Disconnect'>, 16, False)}
'cmd_by_id:'
{16: (<class '__main__.Hello'>, 16, False),
 17: (<class '__main__.Disconnect'>, 16, False),
 18: (<class '__main__.Ping'>, 16, False),
 19: (<class '__main__.Pong'>, 16, False)}
DEBUG:P2PProtocol:updating commands for <__main__.P2PProtocol object at 0x7f0647032fd0>
XXXXX (<class '__main__.Hello'>, 16, True)
XXXXX (<class '__main__.Ping'>, 16, True)
XXXXX (<class '__main__.Pong'>, 16, True)
XXXXX (<class '__main__.Disconnect'>, 16, True)
'commands:'
[(<class '__main__.Hello'>, 16, True),
 (<class '__main__.Ping'>, 16, True),
 (<class '__main__.Pong'>, 16, True),
 (<class '__main__.Disconnect'>, 16, True)]
'cmd_by_type:'
{<class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Hello'>, 16, True),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Ping'>, 16, True),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Pong'>, 16, True),
 <class '__main__.init_command_class.<locals>._cmd_class'>: (<class '__main__.Disconnect'>, 16, True)}
'cmd_by_id:'
{16: (<class '__main__.Hello'>, 16, True),
 17: (<class '__main__.Disconnect'>, 16, True),
 18: (<class '__main__.Ping'>, 16, True),
 19: (<class '__main__.Pong'>, 16, True)}
INFO:main:========================================================================
INFO:main:base class instance: <__main__.Protocol object at 0x7f0647032dd8>
INFO:main:p2p class instances: [<__main__.P2PProtocol object at 0x7f0647032e48>, <__main__.P2PProtocol object at 0x7f0647032e80>, <__main__.P2PProtocol object at 0x7f0647032fd0>]
INFO:main:command classes: {(<class '__main__.Hello'>, 16, False): (<class '__main__.Hello'>, 16, False), (<class '__main__.Ping'>, 16, False): (<class '__main__.Ping'>, 16, False), (<class '__main__.Pong'>, 16, False): (<class '__main__.Pong'>, 16, False), (<class '__main__.Disconnect'>, 16, False): (<class '__main__.Disconnect'>, 16, False), (<class '__main__.Hello'>, 16, True): (<class '__main__.Hello'>, 16, True), (<class '__main__.Ping'>, 16, True): (<class '__main__.Ping'>, 16, True), (<class '__main__.Pong'>, 16, True): (<class '__main__.Pong'>, 16, True), (<class '__main__.Disconnect'>, 16, True): (<class '__main__.Disconnect'>, 16, True)}
INFO:main:command count across all protocol instances: 8
INFO:main:<__main__.Protocol object at 0x7f0647032dd8> supports Hello: False
INFO:main:<__main__.P2PProtocol object at 0x7f0647032e48> supports Hello: True
INFO:main:(<class '__main__.Hello'>, 16, False) 16 False
INFO:main:(<class '__main__.Ping'>, 16, False) 18 False
INFO:main:(<class '__main__.Pong'>, 16, False) 19 False
INFO:main:(<class '__main__.Disconnect'>, 16, False) 17 False
INFO:main:<__main__.P2PProtocol object at 0x7f0647032e80> supports Hello: True
INFO:main:(<class '__main__.Hello'>, 16, False) 16 False
INFO:main:(<class '__main__.Ping'>, 16, False) 18 False
INFO:main:(<class '__main__.Pong'>, 16, False) 19 False
INFO:main:(<class '__main__.Disconnect'>, 16, False) 17 False
INFO:main:<__main__.P2PProtocol object at 0x7f0647032fd0> supports Hello: True
INFO:main:(<class '__main__.Hello'>, 16, True) 16 True
INFO:main:(<class '__main__.Ping'>, 16, True) 18 True
INFO:main:(<class '__main__.Pong'>, 16, True) 19 True
INFO:main:(<class '__main__.Disconnect'>, 16, True) 17 True