Meta classes - real example

[Mr. Wrobel]

W dniu 17.10.2016 o 18:16, Chris Angelico pisze:
> On Tue, Oct 18, 2016 at 3:03 AM, Mr. Wrobel <mr at e-wrobel.pl> wrote:
>> Hi,
>>
>> I am looking for an example of metaclass usage. Especially I am interestet
>> in manipulating instance variables, for example:
>>
>> My class:
>> class MrMeta(type):
>>         pass
>>
>> class Mr(object):
>>         __metaclass__ = MrMeta
>>
>>         def __init__(self):
>>                 self.imvariable = 'Zmienna self'
>>
>>         def aome method(self):
>>                 print 'I am in instance'
>>
>> So in general, I would like to create a mechanism, that is changing value
>> for self.imvariable to capital letters and this should be included in my
>> metaclass called MrMeta(type).
>>
>> Can you guide me please?
>
> Are you sure you can't just use a descriptor, such as @property?
>
> class Mr(object):
>     @property
>     def imvariable(self):
>         return self._imvariable
>     @imvariable.setter
>     def imvariable(self, value):
>         self._imvariable = str(value).upper()
>
> ChrisA
>
Hi,

I am sure that I can do that with setter/getter, but I want to be closer 
to black magic, that is why I wanted to inlcude Metaclasses.

I know how to acomplish that for class variables, but don;t have any 
idea how to instance.

Mr. Wrobel