Subclassing and built-in methods in Python

问题

For convenience, I wanted to subclass socket to create an ICMP socket:

class ICMPSocket(socket.socket):
    def __init__(self):
        socket.socket.__init__(
            self, 
            socket.AF_INET,
            socket.SOCK_RAW,
            socket.getprotobyname("icmp"))

    def sendto(self, data, host):
        socket.socket.sendto(self, data, (host, 1))

However, I can't override socket.sendto:

>>> s = icmp.ICMPSocket()
>>> s.sendto
<built-in method sendto of _socket.socket object at 0x100587f00>

This is because sendto is a "built-in method". According to the data model reference, this is "really a different disguise of a built-in function, this time containing an object passed to the C function as an implicit extra argument."

My question: is there anyway to override built-in methods when subclassing?

[Edit] Second question: if not, why not?

回答1:

I know this doesn't answer your question, but you could put the socket into an instance variable. This is what Nobody also suggested in the comments.

class ICMPSocket():
    def __init__(self):
        self.s = socket.socket(
            socket.AF_INET,
            socket.SOCK_RAW,
            socket.getprotobyname("icmp"))
    def sendto(self, data, host):
        self.s.sendto(data, (host, 1))
    def __getattr__(self, attr):
        return getattr(self.s, attr)

回答2:

Re-edit : My first solution wasn't working, and after straggling with this for sometime , i can conclude that in the case of python socket when you can say that aggregation is much better than inheriting but in case you want to know how you can do it using inheritance check this code:

import socket


class ICMPSocket(socket.socket):
    def __init__(self):

        self._sock = socket.socket(
                        socket.AF_INET,
                        socket.SOCK_RAW,
                        socket.getprotobyname("icmp"))

        # Delete the methods overrited by the socket initializer to make
        # possible defining our own.
        for attr in socket._delegate_methods:
            try:
                delattr(self, attr)
            except AttributeError:
                pass

    def sendto(self, data, flags, addr):
        return self._sock.sendto(data, flags, (addr, 1))

icmp = ICMPSocket()

print icmp.sendto('PING', 0, '127.0.0.1')

来源：https://stackoverflow.com/questions/6976094/subclassing-and-built-in-methods-in-python

标签

python

subclassing