Marco Buttu wrote:
> 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),
> }
Just add
positiveCheck = staticmethod(positiveCheck)
at this point and everything should work in both Python 2 and 3.
Alternatively use Steven's callable_staticmethod as a decorator.
>
> 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.
PS: AttributeErrors should be raised when an attribute does not exist or
cannot be set; I recommend that you raise a ValueError in positiveCheck().
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