extender method

[Simon Forman]

davehowey at f2s.com wrote:
> 'Learning Python' by Lutz and Ascher (excellent book by the way)
> explains that a subclass can call its superclass constructor as
> follows:
>
> class Super:
>    def method(self):
>    # do stuff
>
> class Extender(Super):
>    def method(self):
>    Super.method(self)   # call the method in super
>    # do more stuff - additional stuff here
>
>
>
> I'm trying to use this for a superclass called 'component' in the
> constructor. I have different types of component (let's say for
> arguments sake resistor, capacitor etc). When I instantiate a new
> resistor, say, I want the constructor to call the constructor within
> the component superclass, and then add some resistor-specific stuff.
>
> Now, this is fine using the above code. Where I'm struggling is with
> argument passing. The following, for example, doesn't seem to work:
>
> class Super:
>    def __init__(self, **kargs):
>    self.data = kargs
>
> class Extender(Super):
>    def __init__(self, **kargs):
>    Super.__init__(self, kargs)   # call the constructor method in Super
>    # do additional extender-specific stuff here
>
> What am I doing wrong? I get:
> TypeError: __init__() takes exactly 1 argument (2 given)
> WARNING: Failure executing file: <main.py>
>
> Dave

Try this:

class Extender(Super):
   def __init__(self, **kargs):
   Super.__init__(self, **kargs)   # call the constructor method in
Super

(add two asterisks to the call.)

Observe, the following script:

def a(*a, **b):
    return a, b

print a(**{'arg':2})
print a(arg=2)
print a({'arg':2})

# Prints:

((), {'arg': 2})
((), {'arg': 2})
(({'arg': 2},), {})


HTH,
~Simon