[Python-Dev] type.__subclasses__() doesn't work

2013-10-09 Thread Antoine Pitrou 

Hello,

Just noticed the following quirk:

 type.__subclasses__()
Traceback (most recent call last):
  File stdin, line 1, in module
TypeError: descriptor '__subclasses__' of 'type' object needs an argument

Yet it would be nice to know about the subclasses of type.

Regards

Antoine.


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Re: [Python-Dev] type.__subclasses__() doesn't work

2013-10-09 Thread Steven D'Aprano 
On Wed, Oct 09, 2013 at 12:20:18PM +0200, Antoine Pitrou wrote:
 
 Hello,
 
 Just noticed the following quirk:
 
  type.__subclasses__()
 Traceback (most recent call last):
   File stdin, line 1, in module
 TypeError: descriptor '__subclasses__' of 'type' object needs an argument
 
 Yet it would be nice to know about the subclasses of type.

py type.__subclasses__(type)
[class 'abc.ABCMeta', class 'string._TemplateMetaclass']


-- 
Steven
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Re: [Python-Dev] type.__subclasses__() doesn't work

2013-10-09 Thread Peter Otten 
Steven D'Aprano wrote:

 On Wed, Oct 09, 2013 at 12:20:18PM +0200, Antoine Pitrou wrote:
 
 Hello,
 
 Just noticed the following quirk:
 
  type.__subclasses__()
 Traceback (most recent call last):
   File stdin, line 1, in module
 TypeError: descriptor '__subclasses__' of 'type' object needs an argument
 
 Yet it would be nice to know about the subclasses of type.
 
 py type.__subclasses__(type)
 [class 'abc.ABCMeta', class 'string._TemplateMetaclass']

The underlying problem seems to be that there is no helper function to 
bypass the instance attribute. Compare:

 class T(type):
... def __len__(self): return 0
... 
 class A(metaclass=T):
... def __len__(self): return 1
... 
 A.__len__()
Traceback (most recent call last):
  File stdin, line 1, in module
TypeError: __len__() missing 1 required positional argument: 'self'
 len(A)
0

So should there be a subclasses() function, in the operator module perhaps?

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Re: [Python-Dev] type.__subclasses__() doesn't work

2013-10-09 Thread Hrvoje Niksic 

On 10/09/2013 02:22 PM, Peter Otten wrote:

py type.__subclasses__(type)
[class 'abc.ABCMeta', class 'string._TemplateMetaclass']


The underlying problem seems to be that there is no helper function to
bypass the instance attribute.


Note that the problem is specific to the type type, which is its own 
metatype. With other types that get __subclasses__ from type, is no 
problem with just calling __subclasses__():


 int.__subclasses__()
[type 'bool']

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