Meta classes - real example

[Mr. Wrobel]

W dniu 18.10.2016 o 16:42, Ethan Furman pisze:
> On 10/17/2016 11:44 PM, Mr. Wrobel wrote:
>
>> Ok,so in general, we could say that using Metclasses is ok for
>> manipulating __new__ but not that what is setting by __init__. Am I
>> right?
>
> No and yes.
>
> In this code (python 2 syntax):
>
> #untested
> class Wonderful(object):
>
>     __metaclass__ = SomeMetaClass
>         diamond = Sparkly(7)
>     club = 9
>
>     def display(self):
>         print "I'm an instance!"
>
> The metaclass controls what happens when Wonderful is created:
>
> - it can add the name 'diamond' to the Sparkly descriptor;
> -  it can change/remove/add other attributes such as club, spade, or
> whatever;
> - it can wrap methods such as display to pre- or post-process calls to it
> - etc.
>
> Once the class (Wonderful, in this example) has been created:
>
> - x = Wonderful()  # metaclass not called
> - x.display()      # metaclass not called
> - x.diamond        # metaclass not called
>
> - list(Wonderful)  # metaclass called (e.g. SomeMetaClass.__iter__(cls) )
>                    # where cls = Wonderful
>
>
> Check out http://stackoverflow.com/a/35730545/208880 for a simple
> demonstration of a metaclass.
>
> --
> ~Ethan~
Thank you Ethan!