[Tutor] dictionary dispatch for object instance attributes question

[Liam Clarke]

Ah, see, I should convince my bosses that I need a Python interpreter.
Of course, then they'd ask what Python was, and why I was thinking
about it at work....

Duh, I was just reading the docs, and I kept thinking that an
attribute was just a class variable.

Thanks, Kent, now I have all sorts of interesting experiments to undertake...


On Sun, 20 Feb 2005 07:26:54 -0500, Kent Johnson <kent37 at tds.net> wrote:
> Liam Clarke wrote:
> > Hi,
> >
> > just an expansion on Brian's query, is there a variant of getattr for
> > instance methods?
> >
> > i.e. class DBRequest:
> >     def __init__(self, fields, action):
> >         self.get(fields)
> >
> >     def get(self, fields):
> >         print fields
> >
> >
> > Instead of self.get in _init__, the value of action to call a
> > function? Or, is it going to have to be dictionary dispatch?
> 
> I don't understand your example, but instance methods are attributes too, so getattr() works with
> them as well as simple values.
> 
> An instance method is an attribute of the class whose value is a function. When you access the
> attribute on an instance you get something called a 'bound method' which holds a reference to the
> actual function and a reference to the instance (to pass to the function as the 'self' parameter).
> You can call a bound method just like any other function. So:
> 
>   >>> class foo:
>   ...   def __init__(self):
>   ...     self.bar = 3
>   ...   def baz(self):
>   ...     print self.bar
>   ...
>   >>> f=foo()
> 
> getattr() of a simple attribute:
>   >>> getattr(f, 'bar')
> 3
> 
> getattr() of an instance method returns a 'bound method':
>   >>> getattr(f, 'baz')
> <bound method foo.baz of <__main__.foo instance at 0x008D5FD0>>
> 
> Calling the bound method (note the added ()) is the same as calling the instance method directly:
>   >>> getattr(f, 'baz')()
> 3
> 
> Of course you can do the same thing with dot notation for attributes:
>   >>> b=f.baz
>   >>> b
> <bound method foo.baz of <__main__.foo instance at 0x008D5FD0>>
>   >>> b()
> 3
> 
> Kent
> 
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> http://mail.python.org/mailman/listinfo/tutor
> 


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