Re: Questions, newbies, and community (was: python terminology on classes)
I stand corrected. I didn't know the background. Thanks for supplying the larger picture. :-) -- http://mail.python.org/mailman/listinfo/python-list
Questions, newbies, and community (was: python terminology on classes)
"Rhodri James" writes: > On Wed, 04 Aug 2010 19:28:48 +0100, Steve Ferg > wrote: > > >> Seriously, we can't keep doing your thinking for you. The answers > >> to all your questions are section 9 of the tutorial. > > > > This is is just the kind of newbie-hostile smart-ass reply that we do > > not want to see on comp.lang.python. […] > With Peng Yu, we've been through that quite a lot. It seemed time to > be a little sharper in the hope that learning might emerge. As someone who generally deplores sharp replies to newbies for the negative effect on the community as a whole and on later newcomers in particular: I have to agree with Rhodri here. This specific case has reached a point where some sharpness is warranted, in my opinion. Peng Yu, please take Rhodri's reply in a spirit of mentoring. You have all the tools at your disposal and they have been pointed out to you numerous times. When asking a question of others, please demonstrate that you have exhausted the existing resources you clearly know you have available to you. -- \ “What we usually pray to God is not that His will be done, but | `\ that He approve ours.” —Helga Bergold Gross | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On Wed, 04 Aug 2010 19:28:48 +0100, Steve Ferg wrote: Seriously, we can't keep doing your thinking for you. The answers to all your questions are section 9 of the tutorial. This is is just the kind of newbie-hostile smart-ass reply that we do not want to see on comp.lang.python. Let's try again: I think that the answers to all your questions are section 9 of the tutorial. http://docs.python.org/py3k/tutorial/index.html Why don't you take a look at it, and then come back again if you still have questions. With Peng Yu, we've been through that quite a lot. It seemed time to be a little sharper in the hope that learning might emerge. -- Rhodri James *-* Wildebeest Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
> Seriously, we can't keep doing your thinking for you. The answers > to all your questions are section 9 of the tutorial. This is is just the kind of newbie-hostile smart-ass reply that we do not want to see on comp.lang.python. Let's try again: I think that the answers to all your questions are section 9 of the tutorial. http://docs.python.org/py3k/tutorial/index.html Why don't you take a look at it, and then come back again if you still have questions. -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On 7/27/2010 1:28 PM, John Nagle wrote: Python 2.6 has a recently added "with" clause, borrowed from LISP, for associating actions with scopes. This is supported for files and locks, but setting your own object up for "with" requires adding special methods to the object. "with" is less convenient and more limited than RAII, but that's the direction Python is going. This may be in preparation for a move to a real garbage collector. I do not remember that being stated as part of the rationale for 'with', but just today someone noted that since 'with' replace most uses of deterministic refcount gc, there is not more scope for changing things, at least for builtin and user classes, as opposed to C-extension classes. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On 7/27/2010 12:17 AM, Bruno Desthuilliers wrote: destructor Python has no real destructor. You can implement a __del__ method that will _eventually_ be called before the instance gets garbage-collected, but you'd rather not rely on it. Also, implementing this method will prevent cycle detection. That's not correct. The Python language reference is at "http://docs.python.org/reference/datamodel.html";. In CPython, either __del__ will be called when the reference count goes to zero, or it won't be called at all. The garbage collector that backs up the reference counting system doesn't delete objects with __del__ methods, because of the usual problems with deletion from a garbage collector. The defined semantics are that loop-free structures are deleted properly, but loops with one object that has a __del__ hang around forever. You can use weak pointers to avoid loops. IronPython and ShedSkin are garbage-collected implementations which have quite different __del__ semantics. That's considered non-standard. In C++, the RAII approach is popular and recommended. In C++, it's routine to create local objects which, when they go out of scope, close a file, unlock a lock, or close a window. It's also widely used in Python, but it's now somewhat deprecated. Python 2.6 has a recently added "with" clause, borrowed from LISP, for associating actions with scopes. This is supported for files and locks, but setting your own object up for "with" requires adding special methods to the object. "with" is less convenient and more limited than RAII, but that's the direction Python is going. This may be in preparation for a move to a real garbage collector. John Nagle -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
Peng Yu a écrit : Hi I'm still kind of confused about the terminology on classes in python. Could you please let me know what the equivalent terms for the following C++ terms? C++ and Python having very different semantics and object models, there's not necessarily a straight one to one mapping. constructor Python uses a smalltalk-like 2 phases instanciation / initialisation scheme. First the "proper" construction (__new__) is called with the class object as first argument, and it must return an unintialised instance of the class. Then the initialiser (__init__) is called on this instance. Now one usually only implements the initialiser, as the default object.__new__ method does what you would expect, so you'll often see people qualifying __init__ as the constructor. destructor Python has no real destructor. You can implement a __del__ method that will _eventually_ be called before the instance gets garbage-collected, but you'd rather not rely on it. Also, implementing this method will prevent cycle detection. member function => method. Note that Python's "methods" are really thin wrappers around function objects that are attributes of the class object. You'll find more on this here: http://wiki.python.org/moin/FromFunctionToMethod member variable => Attribute virtual member function All Python's methods are virtual. function => function !-) Note that in Python, functions and classes are objects. I think that C++ "function" is equivalent to python "function" and C++ "member function" is equivalent to python "method". But I couldn't locate where the original definitions of the corresponding python terms in the manual as these term appear many times. Could you please point me where to look for the definition of these python corresponding terms? You just cannot directly translate C++ into Python, and while there are similarities trying to write C++ in Python will not get you very far. -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On Tue, 27 Jul 2010 01:15:08 +0200, Thomas Jollans wrote: > http://docs.python.org/py3k/reference/datamodel.html should answer all > your questions. It should, but as far as I can tell it doesn't. If it defines "attribute" or "method", I can't find it. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On Mon, 26 Jul 2010 16:52:06 -0500, Peng Yu wrote: > Could you please let me know what the equivalent terms for the following > C++ terms? > > constructor > destructor > member function > member variable > virtual member function > function (1) Python new-style classes have a constructor __new__ and an initialiser __init__. Some people describe both as constructors, but that's strictly incorrect because the instance has already been constructed by the time __init__ is called. (Old-style classes don't have __new__, only __init__.) (2) Python destructors are called __del__ , but you shouldn't use them unless you really know what you are doing. (3) "Member functions" are methods. (4) "Member variables" are attributes. If you have to distinguish between attributes which live on the instance from one that lives on the class, "instance attribute" and "class attribute". (5) I believe that all methods in Python are virtual. (6) Function. > I think that C++ "function" is equivalent to python "function" and C++ > "member function" is equivalent to python "method". But I couldn't > locate where the original definitions of the corresponding python terms > in the manual as these term appear many times. Could you please point me > where to look for the definition of these python corresponding terms? I believe you are right, but I can't find a definition of C++ "member function" that makes sense. Can you please point me where to look for the definition of these C++ terms? I don't believe the Python Language Reference explicitly defines terms such as "attribute" and "method", but the tutorial may help: http://docs.python.org/tutorial/classes.html Quote: In C++ terminology, all class members (including the data members) are public, and all member functions are virtual. Note: although the docs occasionally use the term "members" for attributes, it is considered more standard to use "attribute" or "method" unless discussing data types defined at the C layer. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On 07/26/10 18:15, Thomas Jollans wrote: destructor http://docs.python.org/py3k/reference/datamodel.html#object.__del__ One small caveat -- IIRC, in Java/C++ the destructor is guaranteed to be called with a certain amount of context. I find Python's __del__ almost useless since things it may rely upon can arbitrarily be destroyed before the __del__ is called. -tkc -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On Mon, 26 Jul 2010 22:52:06 +0100, Peng Yu wrote: Hi I'm still kind of confused about the terminology on classes in python. Could you please let me know what the equivalent terms for the following C++ terms? Seriously, we can't keep doing your thinking for you. The answers to all your questions are section 9 of the tutorial. -- Rhodri James *-* Wildebeeste Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: python terminology on classes
On 07/26/2010 11:52 PM, Peng Yu wrote: > Hi > > I'm still kind of confused about the terminology on classes in python. > > Could you please let me know what the equivalent terms for the > following C++ terms? > > constructor constructor. This consists of the class constructor method, __new__, and of the instance initialization method, __init__ In practice, __init__ is really "the constructor". http://docs.python.org/py3k/reference/datamodel.html#object.__new__ > destructor destructor. http://docs.python.org/py3k/reference/datamodel.html#object.__del__ > member function method. Look for "instance method" below http://docs.python.org/py3k/reference/datamodel.html#the-standard-type-hierarchy> > member variable attribute, instance attribute, instance variable. > virtual member function all methods are virtual. > function function. > I think that C++ "function" is equivalent to python "function" and C++ > "member function" is equivalent to python "method". But I couldn't > locate where the original definitions of the corresponding python > terms in the manual as these term appear many times. Could you please > point me where to look for the definition of these python > corresponding terms? http://docs.python.org/py3k/reference/datamodel.html should answer all your questions. -- http://mail.python.org/mailman/listinfo/python-list
python terminology on classes
Hi I'm still kind of confused about the terminology on classes in python. Could you please let me know what the equivalent terms for the following C++ terms? constructor destructor member function member variable virtual member function function I think that C++ "function" is equivalent to python "function" and C++ "member function" is equivalent to python "method". But I couldn't locate where the original definitions of the corresponding python terms in the manual as these term appear many times. Could you please point me where to look for the definition of these python corresponding terms? -- Regards, Peng -- http://mail.python.org/mailman/listinfo/python-list
