Re: Why there is a parameter named self for classmethod function?
Terry Reedy a écrit : Kurt Symanzik wrote: But you might consider decorating the method as a static method instead since in your example you are not using the parameter at all. A static method would not require a parameter. @staticmethod def print_hello(): print hello Functions that refer to neither the class nor an instance thereof can usually be moved outside the class altogether. Python is not Java. Indeed. But there are a couple uses for staticmethods - one of them being polymorphic dispatch on the receiver object. And yes, I know, modules are objects too, but this is not always an option (legacy code, integration with a framework etc). -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
On May 8, 7:52 pm, Steven D'Aprano st...@remove-this- cybersource.com.au wrote: On Thu, 07 May 2009 04:27:15 -0700, Aaron Brady wrote: Can be, but if there's reason enough to keep it with a class, there's no reason not to. That's a bit of hyperbole; the usual reasons such as code bloat, namespace bloat, maintainability etc. all weigh against it. It's just that the benefits weigh heavier. I'm not sure I understand. Whether the function is in the class or extracted out into the module, it is exactly the same function. (Apart from an extra level of indentation, and either an unused self parameter or a @staticmethod line.) Same amount of code, same difficulty of maintainability. Namespace bloat is also the same, the only difference being which namespace is bloated: the class or the method. -- Steven My post was a little harsh. I meant to say that I think I got your idea, but the form it came in was a tautology. Its form was X if not not X. Tautologies come across as particularly low bandwidth in writing, though they do have some content in context. I observe people say them a lot too: 'it is what it is', 'if I want to I want to', 'two bucks is two bucks', etc. Some of the context comes from the partial conventional asymmetry of sentences in English between subject and predicate (nominative and accusative), though there is none in logic. Not to mention, 'hyperbole' isn't the word for what I was thinking either... ahem. The best place for such a function between those two choices can depend on many things, some of which are matters of taste. If the definition occurs in the class, it may be more convenient to read or edit. That difference is pretty negligible. There is semantic difference to inherited classes: whether you have to import the class or the class /and/ the function. Then when it is called, the form will be either 'class.methodA' or just 'methodA', which makes a difference in readability (obviousness) elsewhere that it is called. being which namespace is bloated: the class or the method. I think you meant 'class or module'. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
On Thu, 07 May 2009 04:27:15 -0700, Aaron Brady wrote: Can be, but if there's reason enough to keep it with a class, there's no reason not to. That's a bit of hyperbole; the usual reasons such as code bloat, namespace bloat, maintainability etc. all weigh against it. It's just that the benefits weigh heavier. I'm not sure I understand. Whether the function is in the class or extracted out into the module, it is exactly the same function. (Apart from an extra level of indentation, and either an unused self parameter or a @staticmethod line.) Same amount of code, same difficulty of maintainability. Namespace bloat is also the same, the only difference being which namespace is bloated: the class or the method. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
On Thu, 07 May 2009 00:39:28 -0400, Terry Reedy wrote: Functions that refer to neither the class nor an instance thereof can usually be moved outside the class altogether. Python is not Java. I believe staticmethod() was mainly added because it is needed for .__new__(), at least in some appearances. Can be, but if there's reason enough to keep it with a class, there's no reason not to. Sometimes I have a class with a few methods that share common code, but that code happens to not include self (or cls). Since the common code is only of interest to that class, even though it doesn't need the instance, I factor the common code out into a method. This would be a good candidate for a staticmethod, only due to laziness I don't usually bother :) -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
On May 7, 1:29 am, Steven D'Aprano ste...@remove.this.cybersource.com.au wrote: On Thu, 07 May 2009 00:39:28 -0400, Terry Reedy wrote: Functions that refer to neither the class nor an instance thereof can usually be moved outside the class altogether. Python is not Java. I believe staticmethod() was mainly added because it is needed for .__new__(), at least in some appearances. Can be, but if there's reason enough to keep it with a class, there's no reason not to. Sometimes I have a class with a few methods that share common code, but that code happens to not include self (or cls). Since the common code is only of interest to that class, even though it doesn't need the instance, I factor the common code out into a method. This would be a good candidate for a staticmethod, only due to laziness I don't usually bother :) -- Steven It's also useful if you want to access the function using the syntax of attributes, as in 'self.amethod' where 'amethod' is a static method. If I understand correctly, no bound method is created if the function is static, and as such, the decorator can increase performance. Can be, but if there's reason enough to keep it with a class, there's no reason not to. That's a bit of hyperbole; the usual reasons such as code bloat, namespace bloat, maintainability etc. all weigh against it. It's just that the benefits weigh heavier. There is something that is 'correct' about it IMO, that is, provides syntax to what is valid semantics in an OO context. That may just be another way of stating the thesis though. -- http://mail.python.org/mailman/listinfo/python-list
Why there is a parameter named self for classmethod function?
Hi, ALL: I have a sample code as bellow: #!/usr/bin/env python class Hello: def __init__(self): print Hello __init__ @classmethod def print_hello(self): print hello Hello.print_hello() If I move self parameter of print_hello away, this code fragment won't work. I am wondering when Hello.print_hello() executes, what value will self be asigned? -- Best Regards -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
On Wed, May 6, 2009 at 7:49 PM, Jianchun Zhou jianchun.z...@gmail.com wrote: Hi, ALL: I have a sample code as bellow: #!/usr/bin/env python class Hello: def __init__(self): print Hello __init__ @classmethod def print_hello(self): print hello Hello.print_hello() If I move self parameter of print_hello away, this code fragment won't work. I am wondering when Hello.print_hello() executes, what value will self be asigned? The class itself will be the value of self (hence the class in classmethod) in that case. For this reason, the parameter is conventionally called cls rather than self, to avoid confusion. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
Jianchun Zhou jianchun.z...@gmail.com wrote on 2009-05-07 10:49:33 AM +0800 I have a sample code as bellow: #!/usr/bin/env python class Hello: def __init__(self): print Hello __init__ @classmethod def print_hello(self): print hello Hello.print_hello() If I move self parameter of print_hello away, this code fragment won't work. I am wondering when Hello.print_hello() executes, what value will self be asigned? The self variable above with be populated with a reference to the class, so it would be more appropriately named cls such as: @classmethod def print_hello(cls): print hello But you might consider decorating the method as a static method instead since in your example you are not using the parameter at all. A static method would not require a parameter. @staticmethod def print_hello(): print hello Kurt -- Kurt Symanzik k...@kbsymanzik.org Skype id: ksymanzik http://kbsymanzik.org -- http://mail.python.org/mailman/listinfo/python-list
Re: Why there is a parameter named self for classmethod function?
Kurt Symanzik wrote: But you might consider decorating the method as a static method instead since in your example you are not using the parameter at all. A static method would not require a parameter. @staticmethod def print_hello(): print hello Functions that refer to neither the class nor an instance thereof can usually be moved outside the class altogether. Python is not Java. I believe staticmethod() was mainly added because it is needed for .__new__(), at least in some appearances. tjr -- http://mail.python.org/mailman/listinfo/python-list
