Using a list as a class parameter

Question

class Interface():
    def __init__(self, localIP, remoteIP, numHops, hops):
        self.localIP = localIP
        self.remoteIP = remoteIP
        self.numHops = numHops
        self.hops = []

I want to create an instance like this:

hops, hopIps = stripRoute(ssh.run("traceroute -I " + str(dstHost.ip), hide=True))
host.interfaces.append(Interface(host.ip, dstHost.ip, hops, hopIps))
print(hops)
print(hopIps)

From the print statements I can see that hopIps has a value and length 1 which is expected. However when I then query the new instance of Interface, only the numHops value was updated, hops remains empty.

Side note: Is it really necessary to have numHops? Shouldn't it always be equal to len(hops)? — glglgl
– glglgl, Commented Nov 20, 2019 at 13:52
If the packet only passes through a switch it wont be recorded as a hop(ttl value of packet wont decrease) and therefore len(hops) would be zero but the numHops value would remain 1 — qz_99
– qz_99, Commented Nov 20, 2019 at 13:59

Cory Kramer · Accepted Answer · 2019-11-20 13:46:46Z

6

You passed a list into __init__ but never used it

class Interface():
    def __init__(self, localIP, remoteIP, numHops, hops):
        self.localIP = localIP
        self.remoteIP = remoteIP
        self.numHops = numHops
        self.hops = []

Just assign your list to the member

class Interface():
    def __init__(self, localIP, remoteIP, numHops, hops):
        self.localIP = localIP
        self.remoteIP = remoteIP
        self.numHops = numHops
        self.hops = hops

answered Nov 20, 2019 at 13:46

Cory Kramer

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1 Comment

gbruenjes Over a year ago

maybe you want to make make a copy of hops like this self.hops = hops.copy() to prevent some unwanted behavior?

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