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Date: Sat, 23 Nov 2013 10:39:44 +0100
From: Marco Buttu <marco.buttu@gmail.com>
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To: python-list@python.org
Subject: Re: Behavior of staticmethod in Python 3
References: <l6povp$ndp$1@speranza.aioe.org> <mailman.3076.1385197282.18130.python-list@python.org>
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On 11/23/2013 10:01 AM, Peter Otten wrote:

>> In Python 3 the following two classes should be equivalent:
> Says who?
>
>> >$ cat foo.py
>> >class Foo:
>> >      def foo():
>> >          pass
>> >      print(callable(foo))
>> >
>> >class Foo:
>> >      @staticmethod
>> >      def foo():
>> >          pass
>> >      print(callable(foo))
>> >
>> >But they do not:
>> >
>> >$ python3 foo.py
>> >True
>> >False
>>
>
> Your script is saying that a staticmethod instance is not a callable object.
> It need not be because
>
> Foo.foo()

Yes, you are right about Python 3. But in Python 2, if I am not going 
wrong, there is not solution, and I need to define a function outside 
the class. For instance:

$ cat config.py
class Configuration(object):

     def positiveCheck(value):
         if not value > 0:
             raise AttributeError('Must be a positive number')

     attributes = {
             # Attribute name: (type, checkrule)
             'myattr': (int, positiveCheck),
     }

     def __setattr__(self, name, value):
         if not name in Configuration.attributes:
             raise AttributeError("Attribute `%s` non allowed." %name)

         expected_type, checkrule = Configuration.attributes[name]
         if not isinstance(value, expected_type):
             raise TypeError('The value %s is not of type %s' \
                     %(value, expected_type.__name__))
         if callable(checkrule):
             print('calling %s(%s)' %(checkrule.__name__, value))
             checkrule(value)

         super(Configuration, self).__setattr__(name, value)

The positive check works fine:

 >>> from config import Configuration
 >>> c = Configuration()
 >>> c.myattr = -10
calling positiveCheck(-10)
Traceback (most recent call last):
     ...
AttributeError: Must be a positive number

But I cannot use the method as a function:

 >>> Configuration.positiveCheck(-10)
Traceback (most recent call last):
     ...
Configuration instance as first argument (got int instance instead).

Furthemore, I cannot use the method as a staticmethod, becase otherwise 
it will not be callable inside the class body.

-- 
Marco Buttu