W dniu 17.10.2016 o 23:23, Ethan Furman pisze:
On 10/17/2016 09:23 AM, Mr. Wrobel wrote:
W dniu 17.10.2016 o 18:16, Chris Angelico pisze:
On Tue, Oct 18, 2016 at 3:03 AM, Mr. Wrobel wrote:

I am looking for an example of metaclass usage. Especially I am
in manipulating instance variables, for example:

My class:
class MrMeta(type):

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
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):
    def imvariable(self):
        return self._imvariable
    def imvariable(self, value):
        self._imvariable = str(value).upper()

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.

Metaclasses work on the class level, not the instance level.  The only*
influnce a metaclass is going to have on instances is changes it makes
while it's creating the class.

For example, MrMeta could set descriptors in Mr when it is creating the
Mr class; it could even put it's own __init__ in the class; but to
affect things like instance variables that are added in methods -- well,
it is possible, but it is *a lot* of work.


* Okay, somebody prove me wrong!  :)

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?


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