[PYTHON] Let's take a look at the Scapy code. Overload of special methods __div__, __getitem__ and so on.

Purpose

I have a little errand, for example, what does the Scapy code look like? What is Scapy? Scapy is a powerful Python-based interactive packet manipulation program and library. (Quote: https://pypi.org/project/scapy/)

Python layman? (I'm not familiar with it), but it was a pretty difficult code for me.

First, ** around the overload of special methods, the code I don't understand **, so I'll make a note of this article.

What I found

All quote codes are https://github.com/secdev/scapy From.

\ _ \ _ Div \ _ \ _ overload

How to use:

    a = IP(dst=dest) / TCP(flags="S", seq=i, sport=65000, dport=55556)
    b = IP(dst=dest)/ICMP()

Action: ** Attach objects with "/". ** **

It is overloaded with code that looks like this:

    def __div__(self, other):
        if isinstance(other, Packet):
            cloneA = self.copy()
            cloneB = other.copy()
            cloneA.add_payload(cloneB)
            return cloneA
        elif isinstance(other, (bytes, str)):
            return self / conf.raw_layer(load=other)
        else:
            return other.__rdiv__(self)

Overload of \ _ \ _ getitem \ _ \ _

How to use:

        seq = pkt[TCP].seq

Action: ** [] to take out a part. ** **

It is overloaded with code that looks like this:

    def __getitem__(self, cls):
        if isinstance(cls, slice):
            lname = cls.start
            if cls.stop:
                ret = self.getlayer(cls.start, nb=cls.stop, **(cls.step or {}))
            else:
                ret = self.getlayer(cls.start, **(cls.step or {}))
        else:
            lname = cls
            ret = self.getlayer(cls)
        if ret is None:
            if isinstance(lname, Packet_metaclass):
                lname = lname.__name__
            elif not isinstance(lname, bytes):
                lname = repr(lname)
            raise IndexError("Layer [%s] not found" % lname)
        return ret

Summary

The above overload looks useful, so it may be used in other modules as well. Information that may be useful is below.

• The method name for a [iii] is \ _ \ _ getitem \ _ \ _.

If you have any comments, please let us know. : candy: There may be a lot of this kind of processing in other languages as well. .. I'm a little confused when the basic symbols (operators) are overloaded for me, who only knows about C.