__slots__ in derived class

[Schüle Daniel]

Hello,

consider this code

  class A(object):
... def __init__(self):
... self.a = 1
... self.b = 2
...
  class B(A):
... __slots__ = [x,y]
...
  b=B()
  b.a
1
  b.b
2
  b.x = 100
  b.y = 100
  b.z = 100

no exception here
does __slots__ nothing when used in derived classes?


 
 
  class Z(object):
... __slots__ = [x,y]
...
  z=Z()
  z.x = 100
  z.y = 100
  z.z = 100
Traceback (most recent call last):
   File stdin, line 1, in ?
AttributeError: 'Z' object has no attribute 'z'
 

here it works like expected

Regards, Daniel

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: __slots__ in derived class

[Kay Schluehr]

Schüle Daniel wrote:
 Hello,

 consider this code

   class A(object):
 ... def __init__(self):
 ... self.a = 1
 ... self.b = 2
 ...
   class B(A):
 ... __slots__ = [x,y]
 ...
   b=B()
   b.a
 1
   b.b
 2
   b.x = 100
   b.y = 100
   b.z = 100

 no exception here
 does __slots__ nothing when used in derived classes?


  
  
   class Z(object):
 ... __slots__ = [x,y]
 ...
   z=Z()
   z.x = 100
   z.y = 100
   z.z = 100
 Traceback (most recent call last):
File stdin, line 1, in ?
 AttributeError: 'Z' object has no attribute 'z'
  

 here it works like expected

 Regards, Daniel

I would expect that A has to define its own __slots__ too.

The following code should work as expected and makes also sense with
the memory optimization considerations that motivated introduction of
the __slots__ variable.

class A(object):
__slots__ = [a,b]
def __init__(self):
self.a = 1
self.b = 2

class B(A):
__slots__ = [x,y]

Kay

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: __slots__ in derived class

[Duncan Booth]

Schüle Daniel wrote:

 consider this code
 
  class A(object):
 ... def __init__(self):
 ... self.a = 1
 ... self.b = 2
 ...
  class B(A):
 ... __slots__ = [x,y]
 ...
  b=B()
  b.a
 1
  b.b
 2
  b.x = 100
  b.y = 100
  b.z = 100
 
 no exception here
 does __slots__ nothing when used in derived classes?

__slots__ is intended as a way to reduce memory consumption. It was never 
intended as a protection mechanism.

The slots which are available in a class only add to the attributes 
available in the base class. You can hide base class slots by defining a 
slot of the same name, but you cannot remove them.

Your base class has a __dict__ attribute and therefore all instances of the 
base class or any derived classes also have a __dict__ attribute.
-- 
http://mail.python.org/mailman/listinfo/python-list

Don't use __slots__ (was Re: __slots__ in derived class)

[Aahz]

In article [EMAIL PROTECTED],
=?ISO-8859-1?Q?Sch=FCle_Daniel?=  [EMAIL PROTECTED] wrote:

does __slots__ nothing when used in derived classes?

Short answer: don't use __slots__ until you're comfortable writing
metaclasses and decorators.  __slots__ are a performance hack strictly
for advanced users, and if you think you need them, you probably don't.
-- 
Aahz ([EMAIL PROTECTED])   * http://www.pythoncraft.com/

19. A language that doesn't affect the way you think about programming,
is not worth knowing.  --Alan Perlis
-- 
http://mail.python.org/mailman/listinfo/python-list