---------- Forwarded message ----------
From: Kenny Li <[EMAIL PROTECTED] >
Date: Feb 13, 2006 11:00 AM
Subject: Re: [Tutor] Instantiate a subClass using an instance of its baseClass
To: Kent Johnson <[EMAIL PROTECTED]>
Yep! I think that is what I want. I did not know enough to do (inside C.__init__() ):
arg1.__class__=C
As to my intent, I want to subclass socket.socket. By doing so, I may get a socket (instance of my baseClass) after it (my subclass) accepts an incoming connection, and I want to use the subclass instance (the client socket) to get an instance of my subclass.
Do you think your solution would work in my socket.socket subclassing case? (I will give it a try to verify, just asking before I even try)
Again, Thanks a lot, Kent!
PS: there is information about __new__(), but there seems not a lot about __class__, could you point me to some web sources about __class__?
On 2/13/06, Kent Johnson <[EMAIL PROTECTED]
> wrote:
Kenny Li wrote:
> Kent:
>
> I forgot to mention that no coping is allowed. Your two options
> essentially are doing copying of the b.
Not really. I make new references to the attributes of b.
It sounds like you want
c = C(b)
to actually convert b to be an instance of C, instead of creating a new
object. Is that right? You can do that it C.__new__ but I wonder why you
want to?
Here is some code that might do what you want:
''' Construction of a derived class from a base class returns the base class
converted to an instance of the derived class '''
class B(object):
''' the baseClass '''
def __init__(self, arg1, arg2):
self.a1=arg1
self.a2=arg2
def __repr__(self):
return 'B(%r, %r)' % (self.a1, self.a2)
class C(B):
''' C is subClass of B '''
def __new__(cls, arg1, arg2=None):
if isinstance(arg1, B):
# If given a B instance, convert it to a C and return it
arg1.__class__ = C
return arg1
return B.__new__(cls, arg1, arg2)
def __init__(self, arg1, arg2=None):
if not isinstance(arg1, B):
B.__init__(self, arg1, arg2)
self.extra="blah blah blah"
def __repr__(self):
return 'C(%r, %r, %r)' % (self.a1, self.a2, self.extra)
b=B(1, 2)
print b
c=C(2, 3)
print c
c=C(b)
print c, (c is b)
print b # b is now a C - it's the same object as c
Kent
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
_______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
