Python - inheriting from old-style classes
inheritance, python, telnet
Solution
You need to call the constructor like this:
telnetlib.Telnet.__init__(self, host, port, timeout)
You need to add the explicit `self` since `telnet.Telnet.__init__` is not a bound method but rather an unbound method, i.e. witout an instance assigned. So when calling it you need to pass the instance explicitely.
>>> Test.__init__
<unbound method Test.__init__>
>>> Test().__init__
<bound method Test.__init__ of <__main__.Test instance at 0x7fb54c984e18>>
>>> Test.__init__()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unbound method __init__() must be called with Test instance as first argument (got nothing instead)
Problem
I am trying to connect via telnet to a laboratory instrument. I'd like to extend the `Telnet` class from the `telnetlib` module in the standard library, to include functions specific to our instrument: ``` import telnetlib class Instrument(telnetlib.Telnet): def __init__(self, host=None, port=0, timeout=5): super(Instrument,self).__init__(host, port, timeout) ``` All I am trying to do in this code is inherit the `__init__` method from the parent class (`telnetlib.Telnet`) and pass on the standard arguments, so I can add things to `__init__` later. This formula has worked for me on other occasions; this time it gives me an error at the `super()` statement when I try to instantiate: ``` TypeError: must be type, not classobj ``` I looked at the source code for telnetlib, and Telnet appears to be an old-style class (it doesn't inherit from `object`) - I'm wondering if this could be the source of my problem? If so, how can it be overcome? I've seen some code examples where the derived class inherits both from the superclass and `object`, though I'm not entirely sure if this is a response to the same problem as me. Full disclosure: I have also tried using `telnetlib.Telnet` in place of `super()`, and `from telnetlib import Telnet` with `Telnet` in place of `super()`. The problem persists in these cases. Thanks!