dumb q: repeated inheritance in python?

[Corey Coughlin]

Hi, here's a silly question. I'm wrote some code a while back that
looks like this:

import types

class Named(object):
def __init__(self,n m=''):
self.iname = ''
self.setnm(nm)
def setnm (self,nm):
if isinstance(nm, types.StringTyp e):
self.iname = nm
else:
raise TypeError, "Name passed to Named isn't a string."
def getnm (self):
return self.iname
name = property(getnm, setnm)

Pretty basic, a name attribute with simple type checking, it works
fine and the code using it is fine. Well, it was, until I came up
with an object that needed two names, with the same basic type
checking. Now the simplistic way to do that would be copy this class
to another class, say Named2, rename the property name2 and be done
with it. On the other hand, having code that's basically an exact
duplicate of other code except for some name changes seems a tad
inelegant. What I'd really like to do is inherit this same object
twice, but the second time rename the objects so that I get 'name2'
instead of 'name'. (And somehow rename the functions, and so on.)

But I can't figure out how to do it. Is there some way to do this? I
suspect there might be some way to do it with metaclasses, but I
haven't really wrapped my head around that stuff yet. Maybe something
with the new 'super' keyword? Beats me. Anyway, any help would be
great, thanks!!!

[John Roth]

"Corey Coughlin" <co************ @attbi.com> wrote in message
news:a8******** *************** ***@posting.goo gle.com...

Hi, here's a silly question. I'm wrote some code a while back that
looks like this:

import types

class Named(object):
def __init__(self,n m=''):
self.iname = ''
self.setnm(nm)
def setnm (self,nm):
if isinstance(nm, types.StringTyp e):
self.iname = nm
else:
raise TypeError, "Name passed to Named isn't a string."
def getnm (self):
return self.iname
name = property(getnm, setnm)

Pretty basic, a name attribute with simple type checking, it works
fine and the code using it is fine. Well, it was, until I came up
with an object that needed two names, with the same basic type
checking. Now the simplistic way to do that would be copy this class
to another class, say Named2, rename the property name2 and be done
with it. On the other hand, having code that's basically an exact
duplicate of other code except for some name changes seems a tad
inelegant. What I'd really like to do is inherit this same object
twice, but the second time rename the objects so that I get 'name2'
instead of 'name'. (And somehow rename the functions, and so on.)

But I can't figure out how to do it. Is there some way to do this? I
suspect there might be some way to do it with metaclasses, but I
haven't really wrapped my head around that stuff yet. Maybe something
with the new 'super' keyword? Beats me. Anyway, any help would be
great, thanks!!!

Why do the two names have to be in the same object instance? I'd
think the simplest approach would be to bind two instances of your
Named class to two different identifiers.

Otherwise, if you actually need some kind of a collection class, I'd
purpose build one: NamedCollection , or some such.

John Roth

[Duncan Booth]

co************@ attbi.com (Corey Coughlin) wrote in
news:a8******** *************** ***@posting.goo gle.com:

What I'd really like to do is inherit this same object
twice, but the second time rename the objects so that I get 'name2'
instead of 'name'. (And somehow rename the functions, and so on.)

I'm not sure if I exactly understood what you want, but does this help?
I think you are asking for two properties that access differently named
attributes but perform the same type checking in each case.

That sounds to me like you want a specialised property which can be done by
subclassing it:

---- begin test.py ----
class Name(property):
def __init__(cls, attrname):

def setnm(self, nm):
if isinstance(nm, str):
setattr(self, attrname, nm)
else:
raise TypeError("Name passed to %s isn't a string" %
self.__class__. __name__)

def getnm(self):
return getattr(self, attrname)

property.__init __(cls, getnm, setnm)
class TwoNamed(object ):
def __init__(self, iname='', jname=''):
self.iname, self.jname = iname, jname

name = Name('iname')
name2 = Name('jname')

x = TwoNamed('ivalu e', 'jvalue')
print "name, name2 =",x.name, x.name2

x.name = 'www'
x.name2 = 'xxx'

print "name, name2 =",x.name, x.name2
print "iname, jname =",x.iname, x.jname

x.name = 42 # Blows up
print x.name # Never reached.
----- end of test.py ----
--
Duncan Booth du****@rcp.co.u k
int month(char *p){return(1248 64/((p[0]+p[1]-p[2]&0x1f)+1)%12 )["\5\x8\3"
"\6\7\xb\1\x9\x a\2\0\4"];} // Who said my code was obscure?

[Corey Coughlin]

Thanks Duncan, that's exactly what I needed! I'm not very familiar
with subclassing properties, I guess I'll play around with it and see
if I can figure it out. But thanks again, it's great code!

------ Corey
Duncan Booth <du****@NOSPAMr cp.co.uk> wrote in message news:<Xn******* *************** *****@127.0.0.1 >...

co************@ attbi.com (Corey Coughlin) wrote in
news:a8******** *************** ***@posting.goo gle.com:

What I'd really like to do is inherit this same object
twice, but the second time rename the objects so that I get 'name2'
instead of 'name'. (And somehow rename the functions, and so on.)

I'm not sure if I exactly understood what you want, but does this help?
I think you are asking for two properties that access differently named
attributes but perform the same type checking in each case.

That sounds to me like you want a specialised property which can be done by
subclassing it:

---- begin test.py ----
class Name(property):
def __init__(cls, attrname):

def setnm(self, nm):
if isinstance(nm, str):
setattr(self, attrname, nm)
else:
raise TypeError("Name passed to %s isn't a string" %
self.__class__. __name__)

def getnm(self):
return getattr(self, attrname)

property.__init __(cls, getnm, setnm)
class TwoNamed(object ):
def __init__(self, iname='', jname=''):
self.iname, self.jname = iname, jname

name = Name('iname')
name2 = Name('jname')

x = TwoNamed('ivalu e', 'jvalue')
print "name, name2 =",x.name, x.name2

x.name = 'www'
x.name2 = 'xxx'

print "name, name2 =",x.name, x.name2
print "iname, jname =",x.iname, x.jname

x.name = 42 # Blows up
print x.name # Never reached.
----- end of test.py ----