Decorator to inject function into __call__ of a class

[Jon Clements]

On 13 Mar, 16:42, Jack Diederich <jackd... at gmail.com> wrote:
> On Sat, Mar 13, 2010 at 11:19 AM, Jon Clements <jon... at googlemail.com> wrote:
> > This is semi-experimental and I'd appreciate opinions of whether it's
> > the correct design approach or not. It seems like a good idea, but it
> > doesn't mean it is.
>
> > I have a class 'A', this provides standard support functions and
> > exception handling.
> > I have 'B' and 'C' which specialise upon 'A'
>
> > What I'd like to achieve is something similar to:
>
> > @inject(B):
> >  def some_function(a, b):
> >     pass # something useful
>
> > The name 'some_function' is completely redundant -- don't need it,
> > don't actually care about the function afterwards, as long as it
> > becomes a __call__ of a 'B' *instance*.
>
> > I've basically got a huge list of functions, which need to be the
> > callable method of an object, and possibly at run-time, so I don't
> > want to do:
>
> > class Something(B):
> >    def __call__(self, etc.. etc...):
> >         pass # do something
>
> > I've got as far as type(somename, (B,), {}) -- do I then __init__ or
> > __new__ the object or...
>
> > In short, the function should be the __call__ method of an object that
> > is already __init__'d with the function arguments -- so that when the
> > object is called, I get the result of the the function (based on the
> > objects values).
>
> I'm not sure exactly what you are asking for, but if what you want is
> a bunch of different objects that vary only by their class's __call__
> you could do it with a function that returns a new class based on A
> but with a new __call__:
>
> def make_new_call_class(base_class, call_func):
>   class NewClass(base_class):
>     def __call__(self, *args, **kw):
>       return call_func(self, *args, *kw)
>   return NewClass
>
> or the return could even be NewClass() [return an instance] if this is
> a one off.
>
> That said, I'm not really sure what this behavior is good for.
>
> -Jack

Cheers Jack for the response.

The behaviour is to not derive from a class, but rather allow
the decorators to do so... so I would like to iterate over
a list of functions (don't care what they're called) and then
inject the function as a method. If needs be at run-time.

Say I have 1000 functions (okay, admittedly over quoted), but
I don't want every programmer to inherit from 'B' or 'C', but
to 'inject'. So the idea is that classes are pre-defined, have
predictable behaviour, *except* the __call__ is different.

You are correct in this. Why do I want that behaviour? ->

- It's easier, no inheriting from a class, when needs not.
- Some integrity (anyone can define a function and 'inject' to the
Management class)
- Easier maintainability - maybe :)

for i in function_list:
    i = inject(function_list)

At the end of the day:
def blah(x, y, z):
   pass

That should be the callable of the object.

Cheers again,

Jon.