per instance descriptors
Hi I have code similar to this: class Input(object): def __init__(self, val): self.value = val def __get__(self, obj, objtype): return self.value def __set__(self, obj, val): # do some checking... only accept floats etc self.value = val class Node(object): a = Input(1) b = Input(2) I realise that a and b are now class attributes - however I want to do this: node1 = Node() node2 = Node() node1.a = 3 node.b = 4 And have them keep these values per instance. However now node1.a is 4 when it should be 3. Basically I want to have the Input class as a gateway that does lots of checking when the attibute is assigned or read. I have had a look at __getattribute__(), but this gets very ugly as I have to check if the attribute is an Input class or not. Also I don't think property() is appropriate is it? All of the attributes will essentially be doing the same thing - they should not have individual set/get commands. Is there any way of doing this nicely in Python? thanks Simon -- http://mail.python.org/mailman/listinfo/python-list
Re: per instance descriptors
George Sakkis wrote: > [EMAIL PROTECTED] wrote: > > >>George Sakkis wrote: >> >>>Simon Bunker wrote: >>> >>> >>>>Hi I have code similar to this: >>>> >>>>class Input(object): >>>> >>>> def __init__(self, val): >>>> self.value = val >>>> >>>> def __get__(self, obj, objtype): >>>> return self.value >>>> >>>> def __set__(self, obj, val): >>>> # do some checking... only accept floats etc >>>> self.value = val >>>> >>>>class Node(object): >>>> >>>>a = Input(1) >>>>b = Input(2) >>>> >>>>I realise that a and b are now class attributes - however I want to do this: >>>> >>>>node1 = Node() >>>>node2 = Node() >>>> >>>>node1.a = 3 >>>>node.b = 4 >>>> >>>>And have them keep these values per instance. However now node1.a is 4 >>>>when it should be 3. >>>> >>>>Basically I want to have the Input class as a gateway that does lots of >>>>checking when the attibute is assigned or read. >>>> >>>>I have had a look at __getattribute__(), but this gets very ugly as I >>>>have to check if the attribute is an Input class or not. >>>> >>>>Also I don't think property() is appropriate is it? All of the >>>>attributes will essentially be doing the same thing - they should not >>>>have individual set/get commands. >>>> >>>>Is there any way of doing this nicely in Python? >>> >>>What about __setattr__ ? At least from your example, checking happens >>>only when you set an attribute. If not, post a more representative >>>sample of what you're trying to do. >>> >>>George >> >>Yes, but I am setting it in the Node class aren't I? Wouldn't I need to >>define __setattr__() in class Node rather than class Input? I don't >>want to do this. Or am I getting confused here? > > > Yes, __setattr__ would be defined in Node and Input would go. It seems > to me that the only reason you introduced Input was to implement this > controlled attribute access, and as you see it doesn't work as you want > it to. Why not define Node.__setattr__ ? > > George > The __setattr__ approach is what I am hoping to avoid. Having the input class means that I just need to assign a class to an attribute rather than having to filter each attribute name - really annoying as there will be several classes similar to Node with different attributes, but which should be handled in the same way. Frankly descriptors seems exactly what I want - but having them as class attributes makes them completely useless! Simon -- http://mail.python.org/mailman/listinfo/python-list
Re: per instance descriptors
Carl Banks wrote: > Simon Bunker wrote: > >>Hi I have code similar to this: >> >>class Input(object): >> >> def __init__(self, val): >> self.value = val >> >> def __get__(self, obj, objtype): >> return self.value >> >> def __set__(self, obj, val): >> # do some checking... only accept floats etc >> self.value = val >> >>class Node(object): >> >> a = Input(1) >> b = Input(2) >> >>I realise that a and b are now class attributes - however I want to do this: >> >>node1 = Node() >>node2 = Node() >> >>node1.a = 3 >>node2.b = 4 >> >>And have them keep these values per instance. However now node1.a is 4 >>when it should be 3. > > [snip] > >>Is there any way of doing this nicely in Python? > > > The easiest way is to store the value in a hidden attribute of the > object. For instance: > > class Input(object): > def __init__(self,default,name): > self.default = default > self.name = name # or, create a name automatically > def __get__(self,obj,objtype): > return getattr(obj,self.name,self.default) > def __set__(self,obj,value): > setattr(obj,self.name,value) > > class Node(object): > a = Input(1,"_a") > b = Input(2,"_b") > > > Carl Banks > This does seem the easiest way - but also a bit of a hack. Would it work to assign to instance variables - each the class attribute sets the instance attribute with the same name? Or would that not work? Simon -- http://mail.python.org/mailman/listinfo/python-list
Python and GLSL
Hi I was wondering if there is a Python module for running GLSL (OpenGL shader language) in OpenGL through Python. I think that Cg is available through PyCg - most likely using PyGame for the OpenGL. Has anyone done this with GLSL shaders? thanks Simon -- http://mail.python.org/mailman/listinfo/python-list
