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How to set a class inheritance at instance creation?
Hi I wonder if you can set what subclass a class should
have at instance creation.
The problem is that I have something like:
class CoreLang():
def AssignVar(self, var, value):
pass
class Lang1(CoreLang):
def AssignVar(self, var, value):
return var, "=", value
class Lang2(CoreLang):
def AssignVar(self, var, value):
return var, "<=", value
class WriteStruct():
def Generate(self, vars):
for var in vars:
print self.AssignVar()
The problem is that I want WriteStruct to sometimes be a subclass of
Lang1 and sometimes
of Lang2.
In the above example I could but the Generate Method in CoreLang. But
in my real
example I also want to able to subclass WriteStruct to be able to easy
customize WriteStruct.
Which I wouldnt be able to do if it was a method in CoreLang.
So in code I would like to write something like:
WriteStruct(Lang1).Generate(vars)
Even better would be that if I in the Lang1 class could
just do WriteStruct().Generate(vars) and Lang1 class would
magically make WriteStruct a subclass of itself.
Cheers,
/T
On May 29, 8:52 pm, glomde <tbr@yahoo.com> wrote:
> Hi I wonder if you can set what subclass a class should > have at instance creation. > The problem is that I have something like:
> class CoreLang():
> def AssignVar(self, var, value):
> pass
> class Lang1(CoreLang):
> def AssignVar(self, var, value):
> return var, "=", value
> class Lang2(CoreLang):
> def AssignVar(self, var, value):
> return var, "<=", value
> class WriteStruct():
> def Generate(self, vars):
> for var in vars:
> print self.AssignVar()
> The problem is that I want WriteStruct to sometimes be a subclass of
> Lang1 and sometimes
> of Lang2.
> In the above example I could but the Generate Method in CoreLang. But
> in my real
> example I also want to able to subclass WriteStruct to be able to easy
> customize WriteStruct.
> Which I wouldnt be able to do if it was a method in CoreLang.
> So in code I would like to write something like:
> WriteStruct(Lang1).Generate(vars)
def __init__(self, SubClass):
self._sub = SubClass()
def Generate(self, vars):
for var in vars:
print self._sub.AssignVar()
This does what you want but isn't inheritance.
> Even better would be that if I in the Lang1 class could
> just do WriteStruct().Generate(vars) and Lang1 class would
> magically make WriteStruct a subclass of itself.
I don't think I understood what you want here.
Ram
Why not just have Lang1 and Lang2 inherit from WriteStruct as well?
On May 29, 8:52 am, glomde <tbr@yahoo.com> wrote:
> Hi I wonder if you can set what subclass a class should > have at instance creation. > The problem is that I have something like:
> class CoreLang():
> def AssignVar(self, var, value):
> pass
> class Lang1(CoreLang):
> def AssignVar(self, var, value):
> return var, "=", value
> class Lang2(CoreLang):
> def AssignVar(self, var, value):
> return var, "<=", value
> class WriteStruct():
> def Generate(self, vars):
> for var in vars:
> print self.AssignVar()
> The problem is that I want WriteStruct to sometimes be a subclass of
> Lang1 and sometimes
> of Lang2.
> In the above example I could but the Generate Method in CoreLang. But
> in my real
> example I also want to able to subclass WriteStruct to be able to easy
> customize WriteStruct.
> Which I wouldnt be able to do if it was a method in CoreLang.
> So in code I would like to write something like:
> WriteStruct(Lang1).Generate(vars)
> Even better would be that if I in the Lang1 class could
> just do WriteStruct().Generate(vars) and Lang1 class would
> magically make WriteStruct a subclass of itself.
> Cheers,
> /T
On 29 Maj, 19:27, "shand@gmail.com" <shand@gmail.com> wrote:
> Why not just have Lang1 and Lang2 inherit from WriteStruct as well?
This wont work I think since if add antoher Class:
class WriteStruct():
def func1(self);
print "Hello2"
def Generate(self):
self.func1()
class WriteStruct2(WriteStruct):
def func1(self);
print "Hello"
def Generate(self):
self.func1()
Den if Lang1, inherit both WriteStruct and WriteStruct2 I will
get name clashes.
In my real code I have very big Generate Method in WriteStruct that
calls submethods.
and thes submethods should be overriden by the subclasses. So I cant
change the name
on the submethods.
> On May 29, 8:52 am, glomde <tbr@yahoo.com> wrote:
> > Hi I wonder if you can set what subclass a class should
> > have at instance creation.
> > The problem is that I have something like:
> > class CoreLang():
> > def AssignVar(self, var, value):
> > pass
> > class Lang1(CoreLang):
> > def AssignVar(self, var, value):
> > return var, "=", value
> > class Lang2(CoreLang):
> > def AssignVar(self, var, value):
> > return var, "<=", value
> > class WriteStruct():
> > def Generate(self, vars):
> > for var in vars:
> > print self.AssignVar()
> > The problem is that I want WriteStruct to sometimes be a subclass of
> > Lang1 and sometimes
> > of Lang2.
> > In the above example I could but the Generate Method in CoreLang. But
> > in my real
> > example I also want to able to subclass WriteStruct to be able to easy
> > customize WriteStruct.
> > Which I wouldnt be able to do if it was a method in CoreLang.
> > So in code I would like to write something like:
> > WriteStruct(Lang1).Generate(vars)
> > Even better would be that if I in the Lang1 class could
> > just do WriteStruct().Generate(vars) and Lang1 class would
> > magically make WriteStruct a subclass of itself.
> > Cheers,
> > /T
On 29 Maj, 19:20, Ramashish Baranwal <ramashish.li@gmail.com>
wrote:
> On May 29, 8:52 pm, glomde <tbr @yahoo.com> wrote: > > Hi I wonder if you can set what subclass a class should
> > have at instance creation.
> > The problem is that I have something like:
> > class CoreLang():
> > def AssignVar(self, var, value):
> > pass
> > class Lang1(CoreLang):
> > def AssignVar(self, var, value):
> > return var, "=", value
> > class Lang2(CoreLang):
> > def AssignVar(self, var, value):
> > return var, "<=", value
> > class WriteStruct():
> > def Generate(self, vars):
> > for var in vars:
> > print self.AssignVar()
> > The problem is that I want WriteStruct to sometimes be a subclass of
> > Lang1 and sometimes
> > of Lang2.
> > In the above example I could but the Generate Method in CoreLang. But
> > in my real
> > example I also want to able to subclass WriteStruct to be able to easy
> > customize WriteStruct.
> > Which I wouldnt be able to do if it was a method in CoreLang.
> > So in code I would like to write something like:
> > WriteStruct(Lang1).Generate(vars)
> class WriteStruct:
> def __init__(self, SubClass):
> self._sub = SubClass()
> def Generate(self, vars):
> for var in vars:
> print self._sub.AssignVar()
> This does what you want but isn't inheritance.
> > Even better would be that if I in the Lang1 class could
> > just do WriteStruct().Generate(vars) and Lang1 class would
> > magically make WriteStruct a subclass of itself.
> I don't think I understood what you want here.
Somhehow in my:
class Lang1(CoreLang):
def Function(self):
WriteStruct().Generate()
Then somehow this WriteStruct should magically know that has been
instantiated in Lang1.
But this is not really needed. Just wondered if it was possible.
> Ram
On May 29, 8:52 pm, glomde <tbr@yahoo.com> wrote:
> Hi I wonder if you can set what subclass a class should > have at instance creation. > The problem is that I have something like:
> class CoreLang():
> def AssignVar(self, var, value):
> pass
> class Lang1(CoreLang):
> def AssignVar(self, var, value):
> return var, "=", value
> class Lang2(CoreLang):
> def AssignVar(self, var, value):
> return var, "<=", value
> class WriteStruct():
> def Generate(self, vars):
> for var in vars:
> print self.AssignVar()
> The problem is that I want WriteStruct to sometimes be a subclass of
> Lang1 and sometimes
> of Lang2.
> In the above example I could but the Generate Method in CoreLang. But
> in my real
> example I also want to able to subclass WriteStruct to be able to easy
> customize WriteStruct.
> Which I wouldnt be able to do if it was a method in CoreLang.
> So in code I would like to write something like:
> WriteStruct(Lang1).Generate(vars)
def __init__(self, SubClass):
self._sub = SubClass()
def Generate(self, vars):
for var in vars:
print self._sub.AssignVar()
> Even better would be that if I in the Lang1 class could
> just do WriteStruct().Generate(vars) and Lang1 class would
> magically make WriteStruct a subclass of itself.
I don't think I understood what you want here.
Ram
glomde schrieb:
> Hi I wonder if you can set what subclass a class should > have at instance creation. > The problem is that I have something like:
> class CoreLang():
> def AssignVar(self, var, value):
> pass
> class Lang1(CoreLang):
> def AssignVar(self, var, value):
> return var, "=", value
> class Lang2(CoreLang):
> def AssignVar(self, var, value):
> return var, "<=", value
> class WriteStruct():
> def Generate(self, vars):
> for var in vars:
> print self.AssignVar()
> The problem is that I want WriteStruct to sometimes be a subclass of
> Lang1 and sometimes
> of Lang2.
> In the above example I could but the Generate Method in CoreLang. But
> in my real
> example I also want to able to subclass WriteStruct to be able to easy
> customize WriteStruct.
> Which I wouldnt be able to do if it was a method in CoreLang.
> So in code I would like to write something like:
> WriteStruct(Lang1).Generate(vars)
> Even better would be that if I in the Lang1 class could
> just do WriteStruct().Generate(vars) and Lang1 class would
> magically make WriteStruct a subclass of itself.
> Cheers,
> /T
>>> def foo(self, blah):
... print self, blah
...
>>> attrs = {'foo': foo}
>>> cls = type('MyCls', (object,), attrs)
>>> cls().foo(4)
<__main__.MyCls object at 0x009E86D0> 4
Changing ``object`` (the tuple contains all bases) will change the
parent. But, better stick to previous solutions. :)
Stargaming
glomde wrote: > Hi I wonder if you can set what subclass a class should > have at instance creation. > The problem is that I have something like:
> class CoreLang():
> def AssignVar(self, var, value):
> pass
> class Lang1(CoreLang):
> def AssignVar(self, var, value):
> return var, "=", value
> class Lang2(CoreLang):
> def AssignVar(self, var, value):
> return var, "<=", value
> class WriteStruct():
> def Generate(self, vars):
> for var in vars:
> print self.AssignVar()
> The problem is that I want WriteStruct to sometimes be a subclass of
> Lang1 and sometimes
> of Lang2.
> In the above example I could but the Generate Method in CoreLang. But
> in my real
> example I also want to able to subclass WriteStruct to be able to easy
> customize WriteStruct.
> Which I wouldnt be able to do if it was a method in CoreLang.
> So in code I would like to write something like:
> WriteStruct(Lang1).Generate(vars)
> Even better would be that if I in the Lang1 class could
> just do WriteStruct().Generate(vars) and Lang1 class would
> magically make WriteStruct a subclass of itself.
It seems that when you create a WriteStruct you should really be passing
its __init__() method the class that you want it to be a "subclass" of,
creating an instance of that class, and then using generic delegation to
that subclass (using a modified __getattr__()) to handle methods that
aren't found in the WriteStruct.
I can see there are circumstances in which this might not work, but I
believe your current ugly intentions reveal a design smell that you
really need to get rid of if you want a clean program.
regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
------------------ Asciimercial ---------------------
Get on the web: Blog, lens and tag your way to fame!!
holdenweb.blogspot.com squidoo.com/pythonology
tagged items: del.icio.us/steve.holden/python
All these services currently offer free registration!
-------------- Thank You for Reading ----------------
glomde wrote: > Hi I wonder if you can set what subclass a class should > have at instance creation. > The problem is that I have something like:
> class CoreLang():
> def AssignVar(self, var, value):
> pass
> class Lang1(CoreLang):
> def AssignVar(self, var, value):
> return var, "=", value
> class Lang2(CoreLang):
> def AssignVar(self, var, value):
> return var, "<=", value
> class WriteStruct():
> def Generate(self, vars):
> for var in vars:
> print self.AssignVar()
> The problem is that I want WriteStruct to sometimes be a subclass of
> Lang1 and sometimes
> of Lang2.
> In the above example I could but the Generate Method in CoreLang. But
> in my real
> example I also want to able to subclass WriteStruct to be able to easy
> customize WriteStruct.
> Which I wouldnt be able to do if it was a method in CoreLang.
> So in code I would like to write something like:
> WriteStruct(Lang1).Generate(vars)
> Even better would be that if I in the Lang1 class could
> just do WriteStruct().Generate(vars) and Lang1 class would
> magically make WriteStruct a subclass of itself.
It seems that when you create a WriteStruct you should really be passing
its __init__() method the class that you want it to be a "subclass" of,
creating an instance of that class, and then using generic delegation to
that subclass (using a modified __getattr__()) to handle methods that
aren't found in the WriteStruct.
I can see there are circumstances in which this might not work, but I
believe your current ugly intentions reveal a design smell that you
really need to get rid of if you want a clean program.
regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
------------------ Asciimercial ---------------------
Get on the web: Blog, lens and tag your way to fame!!
holdenweb.blogspot.com squidoo.com/pythonology
tagged items: del.icio.us/steve.holden/python
All these services currently offer free registration!
-------------- Thank You for Reading ----------------
On 29 Maj, 22:45, Steve Holden <s@holdenweb.com> wrote:
> glomde wrote: > > Hi I wonder if you can set what subclass a class should > > have at instance creation. > > The problem is that I have something like:
> > class CoreLang():
> > def AssignVar(self, var, value):
> > pass
> > class Lang1(CoreLang):
> > def AssignVar(self, var, value):
> > return var, "=", value
> > class Lang2(CoreLang):
> > def AssignVar(self, var, value):
> > return var, "<=", value
> > class WriteStruct():
> > def Generate(self, vars):
> > for var in vars:
> > print self.AssignVar()
> > The problem is that I want WriteStruct to sometimes be a subclass of
> > Lang1 and sometimes
> > of Lang2.
> > In the above example I could but the Generate Method in CoreLang. But
> > in my real
> > example I also want to able to subclass WriteStruct to be able to easy
> > customize WriteStruct.
> > Which I wouldnt be able to do if it was a method in CoreLang.
> > So in code I would like to write something like:
> > WriteStruct(Lang1).Generate(vars)
> > Even better would be that if I in the Lang1 class could
> > just do WriteStruct().Generate(vars) and Lang1 class would
> > magically make WriteStruct a subclass of itself.
> You should rethink your program design.
> It seems that when you create a WriteStruct you should really be passing
> its __init__() method the class that you want it to be a "subclass" of,
> creating an instance of that class, and then using generic delegation to
> that subclass (using a modified __getattr__()) to handle methods that
> aren't found in the WriteStruct.
I needed to solve it with inheritance.
Didnt think of the possibility to modify getattr to make
the delegation be much nicer. Thanks for the tip
> I can see there are circumstances in which this might not work, but I
> believe your current ugly intentions reveal a design smell that you
> really need to get rid of if you want a clean program.
> regards
> Steve
> --
> Steve Holden +1 571 484 6266 +1 800 494 3119
> Holden Web LLC/Ltd http://www.holdenweb.com
> Skype: holdenweb http://del.icio.us/steve.holden
> ------------------ Asciimercial ---------------------
> Get on the web: Blog, lens and tag your way to fame!!
> holdenweb.blogspot.com squidoo.com/pythonology
> tagged items: del.icio.us/steve.holden/python
> All these services currently offer free registration!
> -------------- Thank You for Reading ----------------
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