[Python-Dev] __slots__ and default values

[Raymond Hettinger]

Was there a reason that __slots__ makes initialized
variables read-only?  It would be useful to have
overridable default values (even if it entailed copying
them into an instance's slots):

class Pane(object):
    __slots__ = ('background', 'foreground', 'size', 'content')
    background = 'black'
    foreground = 'white'
    size = (80, 25)

p = Pane()
p.background = 'light blue'     # override the default
assert p.foreground == 'white' # other defaults still in-place



Raymond Hettinger
    




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>>> class A(object):
 __slots__ = ('x',)
 x = 1
 
>>> class B(object):
 __slots__ = ('x',)

>>> A().x = 2
Traceback (most recent call last):
  File "<pyshell#6>", line 1, in ?
    A().x = 2
AttributeError: 'A' object attribute 'x' is read-only
>>> B().x = 2