howto overload with a NOP (empty statement)

[Bruno Desthuilliers]

Stef Mientki a écrit :
> How should I overload / disable a method ?
> In the example below I have defined the class "Power_Supply", derived 
> from baseclass "device".

<off>
Naming conventions are to use CamelCase for class names. So it would be 
better to name your classes 'PowerSupply' (no '_') and 'Device'. You're 
of course free to use whatever naming convention you want, including no 
convention at all, but Python relies *a lot* on naming conventions...
</off>

> The baseclass has a method "execute",

<off>
Do you know that Python let you define your own 'callable' objects ?

class SomeCallable(object):
   def __init__(self, name):
     self.name = name
   def __call__(self):
     print "wow, %s has been called" % self.name

foo = SomeCallable('foo')
foo()

This may or not make sens in the context of your application, but 
whenever you find yourself naming a method 'execute', it might be worth 
asking yourself if the object should in fact be a callable...
</off>

> which will be implemented in most 
> derived classes, but not in all.
 >
> Now apparently it's not allowed to overload a method with an empty 
> statement.
> I could write a nonsense dummy statement, like "A= 3", but isn't there 
> another way ?

the 'pass' statement

def noop():
   pass

> thanks, Stef Mientki
> 
> class device:
>   def execute (self):
>     print 'execute not yet implemented for', self.Name

The usual idiom for 'pure virtual methods' is to raise a 
NotImplementedError. Now if it's ok for a subclass to implement the 
method as a no-op, why not just implement it as a no-op in the base 
class itself ?