different instances with different data descriptors with the same name

[Fabrizio Pollastri]

Data descriptors are set as attributes of object types. So if one has many
instances of the same class and wants each instance to have a different property
(data descriptor) that can be accessed with a unique attribute name, it seems to
me that there is no solution with data descriptors. There is any workaround to
this? Thank in advance for any help.

F. Pollastri

 

[Peter Otten]

Data descriptors are set as attributes of object types. So if one has many
instances of the same class and wants each instance to have a different
property (data descriptor) that can be accessed with a unique attribute
name, it seems to me that there is no solution with data descriptors.
There is any workaround to this? Thank in advance for any help.

You can invent a naming convention and then invoke the getter/setter
explicitly:
.... def __getattr__(self, name):
.... if not name.startswith("_prop_"):
.... return getattr(self, "_prop_" + name).__get__(self)
.... raise AttributeError(name)
....Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 4, in __getattr__
1764

But what are you really trying to do?

Peter

 

[grflanagan]

Data descriptors are set as attributes of object types. So if one has many
instances of the same class and wants each instance to have a different property
(data descriptor) that can be accessed with a unique attribute name, it seems to
me that there is no solution with data descriptors. There is any workaround to
this? Thank in advance for any help.

F. Pollastri

If you explain your intent you might get some good advice. Here's one
idea:

class Descriptor(object):
    val = 0

    def __init__(self, initval=0):
        self.val = initval

    def __get__(self, obj, objtype):
        return '%05d' % self.val

    def __set__(self, obj, val):
        self.val = val

def Factory(attrname, initval=0):

    class Obj(object):
        pass

    setattr(Obj, attrname, Descriptor(initval))

    return Obj

X = Factory('x')
Y = Factory('y', 1)

obj1 = X()

print obj1.x

obj2 = Y()

print obj2.y

obj2.y = 5

print obj2.y

print obj2.x

Outputs:

00000
00001
00005
Traceback (most recent call last):
...
AttributeError: 'Obj' object has no attribute 'x'


Gerard