Re: Can you create an instance of a subclass with an existing instance of the base class?
Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], bruno at modulix [EMAIL PROTECTED] wrote: Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], bruno at modulix [EMAIL PROTECTED] wrote: Lawrence D'Oliveiro wrote: (snip) I think you're taking Python's OO-ness too seriously. One of the strengths of Python is that it can _look_ like an OO language without actually being OO. According to which definition of OO ? Isn't there one? Your claim that Python _look_ like an OO language without actually being OO implicitely relies on a definition of OO - or is just meaningless. Which nicely evades answering the question. Well I have to say you are also nicely evading answering the question, which is enough to make me suspect your are trolling (deliberately asking contentious questions for the purposes of creating futile argument and discussion). If you *aren't* trolling then what's your objection to saying what led you to make the assertion that Python could look like an OO language without being one? But sine you say later that Python objects are basically dictionaries it's clear your understanding of Python isn't terribly complete, which might cast doubt on your understanding of object orientation. For the record, Python *is* an object-oriented language, but it happens to offer convenient features for procedural programming as well. Since these features are orthogonal to its OO features, the fact that they exist doesn't stop Python from being an OO language. So why do you assert that it merely looks like one? regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Love me, love my blog http://holdenweb.blogspot.com Recent Ramblings http://del.icio.us/steve.holden -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In [EMAIL PROTECTED], Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], Bruno Desthuilliers [EMAIL PROTECTED] wrote: Nope. I mean : they don't overuse OO, they overuse *classes*. AFAIK, OO means *object* oriented - not class oriented. Oh great. Now we have someone redefining the concept of OO to evade the point I was making. There are OO languages that don't even have a notion of class. Sounds like stuff I was doing in C (a non-OO language) years ago. Unless you want to count C as an OO language, I think you're going to have to retract this claim. That sounds like stuff you do in a language that has objects but no classes. As C has no objects I would not count it as an OO language. But I count Io as an OO language:: #!/usr/bin/env io Foo := Object clone Foo value := 42 Foo setValue := method(newValue, self value = newValue; self) Foo beep := method(beep linePrint) Foo asString := method(I'm a Foo. My value is .. self value) Bar := Foo clone Bar asString := method(I'm a Bar and .. super asString) foo := Foo clone foo beep foo asString linePrint bar := Bar clone setValue(23) bar beep bar asString linePrint Output is: beep I'm a Foo. My value is 42 beep I'm a Bar and I'm a Foo. My value is 23 That's OO IMHO. Clonable objects that know their ancestors so you can build an object hierarchy. Missing attributes are looked up in the ancestors and one can explicitly look up the inheritance tree with ``super``. There are no classes, just four objects. Convention in naming and usage makes two of them something like templates or classes for new objects but they are in no way special. Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In article [EMAIL PROTECTED], Bruno Desthuilliers [EMAIL PROTECTED] wrote: Sandra-24 a écrit : Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], Sandra-24 [EMAIL PROTECTED] wrote: Now that is a clever little trick. I never would have guessed you can assign to __class__, Python always surprises me in it's sheer flexibility. That's because you're still thinking in OO terms. It's not quite as simple as all that. I agree that people, escpecially people with a Java (ew) background overuse OO, when there's often simpler ways of doing things. Nope. I mean : they don't overuse OO, they overuse *classes*. AFAIK, OO means *object* oriented - not class oriented. Oh great. Now we have someone redefining the concept of OO to evade the point I was making. There are OO languages that don't even have a notion of class. Sounds like stuff I was doing in C (a non-OO language) years ago. Unless you want to count C as an OO language, I think you're going to have to retract this claim. However in this case I'm simply getting an object (an mp_request object from mod_python) passed into my function, and before I pass it on to the functions that make up and individual web page it is modified by adding members and methods to add functionality. Which is a well-known design pattern called decorator. If you have to think of it as a design pattern, that means you haven't figured out the code reuse angle yet. -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In article [EMAIL PROTECTED], bruno at modulix [EMAIL PROTECTED] wrote: Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], bruno at modulix [EMAIL PROTECTED] wrote: Lawrence D'Oliveiro wrote: (snip) I think you're taking Python's OO-ness too seriously. One of the strengths of Python is that it can _look_ like an OO language without actually being OO. According to which definition of OO ? Isn't there one? Your claim that Python _look_ like an OO language without actually being OO implicitely relies on a definition of OO - or is just meaningless. Which nicely evades answering the question. -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Lawrence D'Oliveiro wrote:
In article [EMAIL PROTECTED],
Bruno Desthuilliers [EMAIL PROTECTED] wrote:
Sandra-24 a écrit :
Lawrence D'Oliveiro wrote:
In article [EMAIL PROTECTED],
Sandra-24 [EMAIL PROTECTED] wrote:
Now that is a clever little trick. I never would have guessed you can
assign to __class__, Python always surprises me in it's sheer
flexibility.
That's because you're still thinking in OO terms.
It's not quite as simple as all that. I agree that people, escpecially
people with a Java (ew) background overuse OO, when there's often
simpler ways of doing things.
Nope. I mean : they don't overuse OO, they overuse *classes*. AFAIK, OO
means *object* oriented - not class oriented.
Oh great. Now we have someone redefining the concept of OO to evade the
point I was making.
redefining ? lol...
There are OO languages that don't even have a notion of class.
Sounds like stuff I was doing in C (a non-OO language) years ago. Unless
you want to count C as an OO language, I think you're going to have to
retract this claim.
I think I'm not going to retract anything. And I think you should learn
a bit more about prototype-based languages.
However in this case I'm simply getting an object (an mp_request object
from mod_python) passed into my function, and before I pass it on to
the functions that make up and individual web page it is modified by
adding members and methods to add functionality.
Which is a well-known design pattern called decorator.
If you have to think of it as a design pattern, that means you haven't
figured out the code reuse angle yet.
Please stop saying non-sense and learn the difference between design and
implementation.
--
bruno desthuilliers
python -c print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in '[EMAIL PROTECTED]'.split('@')])
--
http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In article [EMAIL PROTECTED], bruno at modulix [EMAIL PROTECTED] wrote: Lawrence D'Oliveiro wrote: (snip) I think you're taking Python's OO-ness too seriously. One of the strengths of Python is that it can _look_ like an OO language without actually being OO. According to which definition of OO ? Isn't there one? -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Lawrence D'Oliveiro wrote:
In article [EMAIL PROTECTED],
bruno at modulix [EMAIL PROTECTED] wrote:
Lawrence D'Oliveiro wrote:
(snip)
I think you're taking Python's OO-ness too seriously. One of the
strengths of Python is that it can _look_ like an OO language without
actually being OO.
According to which definition of OO ?
Isn't there one?
Your claim that Python _look_ like an OO language without actually
being OO implicitely relies on a definition of OO - or is just
meaningless. So I ask you: what definition of OO do you use to support
your claim ?
--
bruno desthuilliers
python -c print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in '[EMAIL PROTECTED]'.split('@')])
--
http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Lawrence D'Oliveiro wrote:
(snip)
I think you're taking Python's OO-ness too seriously. One of the
strengths of Python is that it can _look_ like an OO language without
actually being OO.
According to which definition of OO ?
--
bruno desthuilliers
python -c print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in '[EMAIL PROTECTED]'.split('@')])
--
http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Lawrence D'Oliveiro wrote: All you want is a dictionary, then. That's basically what Python objects are. Yes, that's it exactly. I made a lazy wrapper for it, and I was really happy with what I was able to accomplish, it turned out to be very easy. Thanks, -Sandra -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Sandra-24 a écrit : Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], Sandra-24 [EMAIL PROTECTED] wrote: Now that is a clever little trick. I never would have guessed you can assign to __class__, Python always surprises me in it's sheer flexibility. That's because you're still thinking in OO terms. It's not quite as simple as all that. I agree that people, escpecially people with a Java (ew) background overuse OO, when there's often simpler ways of doing things. Nope. I mean : they don't overuse OO, they overuse *classes*. AFAIK, OO means *object* oriented - not class oriented. There are OO languages that don't even have a notion of class. However in this case I'm simply getting an object (an mp_request object from mod_python) passed into my function, and before I pass it on to the functions that make up and individual web page it is modified by adding members and methods to add functionality. Which is a well-known design pattern called decorator. (snip) Sadly I'm unable to create it as a python object first, because it's created by the time my code comes into play. So I have to resort to using the new module to add methods. This is OK IMHO. It works, but it has to be redone for every request, Is this really a problem ? I thought moving the extra functionality to another object would simplify the task. A better way might be to contain the mp_request within another object and use __getattr__ to lazily copy the inner object. I'd probably have to first copy those few fields that are not read-only or use __setattr__ as well. Why copy ? You could as well just use composition/delegation (also using __getattr__ - and BTW, this is another possible implementation of the decorator pattern). -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Sandra-24 wrote: Now that is a clever little trick. I never would have guessed you can assign to __class__, Python always surprises me in it's sheer flexibility. In this case it doesn't work. TypeError: __class__ assignment: only for heap types I suspect that's because this object begins its life in C code. The technique of using the __class__.__subclasses__ also fails: TypeError: cannot create 'B' instances This seems more complex than I thought. Can one do this for an object that beings it's life in C? The restriction originates in the metaclass. Perhaps you can use a customized metaclass that allows subclass assignment, but I don't know enough about Python's internals to tell you how/whether that is possible. An alternative might be that you always start out with a subclass coded in Python: abc = tuple(abc) abc.__class__ = tuple Traceback (most recent call last): File stdin, line 1, in ? TypeError: __class__ assignment: only for heap types class Tuple(tuple): pass ... class Subclass(Tuple): ... first = property(lambda self: self[0]) ... abc = Tuple(abc) abc.__class__ = Subclass abc.first 'a' In the example a Tuple should be able to do everything a tuple can do; because Tuple is coded in Python you can also change the __class__. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Lawrence D'Oliveiro wrote: In article [EMAIL PROTECTED], Sandra-24 [EMAIL PROTECTED] wrote: Now that is a clever little trick. I never would have guessed you can assign to __class__, Python always surprises me in it's sheer flexibility. That's because you're still thinking in OO terms. It's not quite as simple as all that. I agree that people, escpecially people with a Java (ew) background overuse OO, when there's often simpler ways of doing things. However in this case I'm simply getting an object (an mp_request object from mod_python) passed into my function, and before I pass it on to the functions that make up and individual web page it is modified by adding members and methods to add functionality. It's not that I'm thinking in OO, but that the object is a convienient place to put things, especially functions that take an mp_request object as their first argument. Sadly I'm unable to create it as a python object first, because it's created by the time my code comes into play. So I have to resort to using the new module to add methods. It works, but it has to be redone for every request, I thought moving the extra functionality to another object would simplify the task. A better way might be to contain the mp_request within another object and use __getattr__ to lazily copy the inner object. I'd probably have to first copy those few fields that are not read-only or use __setattr__ as well. Thanks, -Sandra -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In article [EMAIL PROTECTED], Sandra-24 [EMAIL PROTECTED] wrote: However in this case I'm simply getting an object (an mp_request object from mod_python) passed into my function, and before I pass it on to the functions that make up and individual web page it is modified by adding members and methods to add functionality. All you want is a dictionary, then. That's basically what Python objects are. -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Sandra-24 wrote: Can you create an instance of a subclass using an existing instance of the base class? Such things would be impossible in some languages or very difficult in others. I wonder if this can be done in python, without copying the base class instance, which in my case is a very expensive object. You can change the class of an instance by assigning to the __class__ attribute. The new class doesn't even need to be a subclass of the old: class A(object): ... def __init__(self, name): ... self.name = name ... def show(self): print self.name ... a = A(alpha) a.show() alpha class B(object): ... def show(self): print self.name.upper() ... a.__class__ = B a.show() ALPHA Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
Now that is a clever little trick. I never would have guessed you can assign to __class__, Python always surprises me in it's sheer flexibility. In this case it doesn't work. TypeError: __class__ assignment: only for heap types I suspect that's because this object begins its life in C code. The technique of using the __class__.__subclasses__ also fails: TypeError: cannot create 'B' instances This seems more complex than I thought. Can one do this for an object that beings it's life in C? Thanks, -Sandra Peter Otten wrote: Sandra-24 wrote: Can you create an instance of a subclass using an existing instance of the base class? Such things would be impossible in some languages or very difficult in others. I wonder if this can be done in python, without copying the base class instance, which in my case is a very expensive object. You can change the class of an instance by assigning to the __class__ attribute. The new class doesn't even need to be a subclass of the old: class A(object): ... def __init__(self, name): ... self.name = name ... def show(self): print self.name ... a = A(alpha) a.show() alpha class B(object): ... def show(self): print self.name.upper() ... a.__class__ = B a.show() ALPHA Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In article [EMAIL PROTECTED], Sandra-24 [EMAIL PROTECTED] wrote: Now that is a clever little trick. I never would have guessed you can assign to __class__, Python always surprises me in it's sheer flexibility. That's because you're still thinking in OO terms. -- http://mail.python.org/mailman/listinfo/python-list
Can you create an instance of a subclass with an existing instance of the base class?
Can you create an instance of a subclass using an existing instance of the base class? Such things would be impossible in some languages or very difficult in others. I wonder if this can be done in python, without copying the base class instance, which in my case is a very expensive object. Any ideas? Thanks, -Sandra -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
In article [EMAIL PROTECTED], Sandra-24 [EMAIL PROTECTED] wrote: Can you create an instance of a subclass using an existing instance of the base class? I think you're taking Python's OO-ness too seriously. One of the strengths of Python is that it can _look_ like an OO language without actually being OO. -- http://mail.python.org/mailman/listinfo/python-list
Re: Can you create an instance of a subclass with an existing instance of the base class?
With new-style classes you can find out a class' subclasses and then you can instantiate the subclass you want. Suppose you have two classes A and B, B is a subclass of A, A is a new-style class. Now you have an A's instance called a, to instance B you can do the following: b = a.__class__.__subclasses__()[0]() -- http://mail.python.org/mailman/listinfo/python-list
