RE: Python, Possibly OO, Terminology Question

  • From: "Ken Perry" <whistler@xxxxxxxxxxxxx>
  • To: <programmingblind@xxxxxxxxxxxxx>
  • Date: Thu, 28 Jul 2011 08:19:08 -0400


The previous answer was wrong.  We used to call functions that return
nothing a procedure but that is in languages like pascal but the following
is the real answer for what is a function verses method.

A function is a piece of code that is called by name. It can be passed data
to operate on (ie. the parameters) and can optionally return data (the
return value).

All data that is passed to a function is explicitly passed.

A method is a piece of code that is called by name that is associated with
an object. In most respects it is identical to a function except for two key
differences.


-----Original Message-----
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Homme, James
Sent: Thursday, July 28, 2011 6:59 AM
To: programmingblind@xxxxxxxxxxxxx
Subject: RE: Python, Possibly OO, Terminology Question

Hi All,
Thanks for trying to answer. I'll just keep coding and eventually I'll
either understand or not.

Jim

-----Original Message-----
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Kerneels Roos
Sent: Thursday, July 28, 2011 3:48 AM
To: programmingblind@xxxxxxxxxxxxx
Subject: Re: Python, Possibly OO, Terminology Question

Jim, and otheres, I agree that "method" and "function" are used 
interchangeably and mean the same thing usually, but I think if you do 
in fact want to distiguish between them you could use "method" for 
something that doesn't return anything (a void function) and use 
"function" when something is returned, but it really doesn't matter much 
since it's just documentation particulars.

In OO terminology people seem to prefer method over function (in my 
experience).

What is more important is to understand the difference between class and 
instance methods, which, coming from Java such as yourself is simple to 
grasp. In computer science it helps to distinguish terminology from 
implementation particulars since languages can and do use varied terms 
for intrinsically the same thing. Some times the language uses the right 
terminology, or the most widely accepted terminology, but ti's not a given.

Now, to get back to Python, it seems there are three types of methods 
(and please correct me here if I'm wrong):

@staticmethod
def some_static_method (param1, param2):
     # do something not involving an instance of the class this method 
is in, except other static items perhaps

So this looks like the class method (OO terminology) which you get in 
Java by adding the "static" method attribute to your method is it not?

@classmethod
def some_class_method (cls):
     # ?? how is this different to @staticmethod ??

Please explain the above.

def some_instance_method (self, param1, param2):
     # can use self. here to reference the instance of the class


This is the normal method you get with Java without adding "static" to 
the method signiture, so a standard instance method in Java would be the 
equivalent of this?


Regards



On 7/27/2011 11:42 PM, David Tseng wrote:
> For the purists out there, classes, functions, methods, procedures,
> etc are all sort of related.  You can think of a class as a function
> in python with some setup/teardown facilities, a closure, and a symbol
> table mapping it's instance variables/functions.  I don't think any
> language shows this better than javascript, but python comes pretty
> close.
>
> But, I think Jamal's right Jim, you should just dive in and see how
> things behave in practice and stop letting me and others confuse you
> :).
>
> On 7/27/11, Q<q@xxxxxxxxxxxxxxxxxx>  wrote:
>> Okay. First, everything is an object as you mentioned. This is
>> somewhat-important.
>> Now, functions vs. methods.
>> Generally in Python function means standalone callable. When I say
>> callable, I'm referring to an object which has a __call__ method.  So
>> when it comes down to it, functions are simply objects that define
>> __call__. But of course, we generally don't create these function
>> objects manually. That's just what happens when the interpreter reads in
>> a def block.
>> So, a function is a regular callable that does not take an instance as
>> its first argument.
>> def test():
>>    print "hello, world!"
>>
>> While you could attach these types of functions to a class:
>> class Tester(object):
>>    pass
>>
>> Tester.test = test
>>
>> note what happens when you instantiate that class and try to use them:
>> t=Tester()
>> t.test()
>> TypeError: test() takes no arguments (1 given)
>> Because Python tries to pass the class instance in as the first argument
>> to that function, and it takes none.
>> Now, there's absolutely no reason you couldn't do something like:
>> def other_test(self):
>>    print "Hi there!"
>>
>> and attach other_test to Tester.
>> And this would actually work just fine. It wouldn't be a true method
>> object, which has a couple of other attributes on it (try dir on a
>> function object and a method object for comparison)
>> Now, you mentioned static methods. How we create these is with the
>> staticmethod decorator.
>> Observe:
>>
>> class SomeClassWithStaticMethods(object):
>>
>>    @staticmethod
>>    def something_inside_the_class_namespace():
>>     return "I was called!"
>>
>> You can call this static method on any class object or instance. So you
>> could go
>>
>> SomeClassWithStaticMethods.something_inside_the_class_namespace()
>> or
>> c = SomeClassWithStaticMethods()
>> c.something_inside_the_class_namespace()
>>
>> but this is rarely-needed, generally better is putting a regular
>> function inside the class's module. This would only be required if you
>> explicitly want to have the function inside the class namespace, I.E. a
>> module with several unrelated classes.
>> Then, we have class methods, marked with the @classmethod decorator.
>> These are extremely-useful. They operate on class objects instead of
>> instance objects.
>>
>> class Something(object):
>>
>>    @classmethod
>>    def do_funky_things_to_the_class(cls):
>>     #You could do all kinds of hackery in here on the class object before
>> its already instantiated or whatever. cls contains the class object, and
>> it's conventional to use cls in this case where self is for instance
>> methods.
>>     cls.some_attribute = 1 #all instances of this class will have
>> some_attribute set to 1 if you call this
>>
>> I hope this untangles things a little. If you don't understand anything
>> feel free to ask, but do do a lot of exploration with dir. also check
>> out the inspect module to let you poke around at the internals and see
>> what's going on a bit under the covers.
>> And if I'm mistaken about anything here, someone on list please-do
>> correct me as this is all stuff I've derived from usage.
>>
>>        Q
>>
>>
>>
>>
>>
>> On 7/27/2011 4:07 PM, Jamal Mazrui wrote:
>>> Yes, I think a function at the module level in Python is like a static
>>> method of that module.  The module, moreover, is like a singleton
object.
>>>
>>> Although these nuances can be interesting to discuss, let me encourage
>>> folks not to get hung up on terminology, thinking that one cannot code
>>> productively until certain theory or terminology is mastered.  I say
>>> try to understand as much theory as one can at the time, but then set
>>> aside a solid grasp of some aspects for now if they seems elusive.
>>>
>>> I think that learning is usually best achieved through an iterative
>>> process that involves both learning and applying ideas.  If one
>>> postpones actual application, there is only so far that one's
>>> understanding can go.  On the other hand, after experiencing the
>>> results of applied understanding, one can try to learn more, apply it
>>> in code, debug, regroup, etc.
>>>
>>> Jamal
>>>
>>> On 7/27/2011 3:45 PM, Homme, James wrote:
>>>> Hi,
>>>> Forgot to copy the list. This sounds like static methods in other
>>>> languages. Is that anywhere in the universe?
>>>>
>>>> Jim
>>>>
>>>> -----Original Message-----
>>>> From: David Tseng [mailto:davidct1209@xxxxxxxxx]
>>>> Sent: Wednesday, July 27, 2011 3:40 PM
>>>> To: programmingblind@xxxxxxxxxxxxx
>>>> Cc: Homme, James
>>>> Subject: Re: Python, Possibly OO, Terminology Question
>>>>
>>>> With respect to python's innate "object orientedness" where
>>>> everything's an object, you can think of functions and methods as
>>>> binding or associated with other objects.  A function or method that's
>>>> "associated" with a class object, takes the class object as its first
>>>> parameter as you stated.  However, you can just as easily bind a
>>>> function or method to a class without that first "self" parameter.
>>>> The distinction lies in what the function or method is bound to.  In
>>>> the former, the function/method binds to an instance of that class
>>>> while the latter binds to the class itself.
>>>>
>>>> For example,
>>>> class foo:
>>>>     def instance(self):
>>>>       pass
>>>>
>>>>     def non_instance():
>>>>       pass
>>>>
>>>> I'd encourage you to not take any of our words for it and try it out
>>>> yourself.  Try typing the follwing into an interpreter.
>>>>>>> foo.non_instance
>>>>>>> foo
>>>>>>> foo.instance
>>>>>>> f = foo()
>>>>>>> f.non_instance
>>>>>>> f.instance
>>>>
>>>>
>>>> On 7/27/11, Jamal Mazrui<empower@xxxxxxxxx>   wrote:
>>>>> I think the terms function, method, procedure, subroutine, or code
>>>>> block
>>>>> are generally synonymous.  They refer to a programming construct that
>>>>> receives 0 or more parameters, executes code with those parameters as
>>>>> data, and then returns 0 or more result values.
>>>>>
>>>>> A particular term may be used to emphasize an aspect of the context
>>>>> under discussion.  For example, a method implies being an aspect of an
>>>>> object.  A subroutine implies that there is no meaningful return
value.
>>>>>     A code block implies an in-line definition with access to
>>>>> surrounding
>>>>> variables.
>>>>>
>>>>> In general, however, I think there are not fine distinctions among
>>>>> these
>>>>> terms.
>>>>>
>>>>> Jamal
>>>>>
>>>>> On 7/27/2011 11:14 AM, Homme, James wrote:
>>>>>> Hi,
>>>>>>
>>>>>> I'm right at the point where I'm concerned about learning this the
>>>>>> wrong
>>>>>> way, so I'm asking now before it's cemented into my head. Is it
>>>>>> appropriate to use the term function and the term method
>>>>>> interchangeably? If so, why? If not, why not? I realize that in
>>>>>> Python,
>>>>>> when you have methods in the definition of a class, they always have
>>>>>> self as the first argument, so that helps you realize that you are
>>>>>> looking at a method. I also know that if you make a program that
>>>>>> has no
>>>>>> classes in it, that you can use functions, and they don't look like
>>>>>> they
>>>>>> are attached to a class, but one of the books I was looking at says
>>>>>> that
>>>>>> everything in Python is an object, even if the code doesn't look like
>>>>>> that, but I'm trying to avoid dragging that into this discussion to
>>>>>> possibly artificially keep concepts separate in order to learn them.
>>>>>>
>>>>>> Thanks.
>>>>>>
>>>>>> Jim
>>>>>>
>>>>>> Jim Homme,
>>>>>>
>>>>>> Usability Services,
>>>>>>
>>>>>> Phone: 412-544-1810.
>>>>>>
>>>>>>
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-- 
Kerneels Roos
Cell: +27 (0)82 309 1998
Skype: cornelis.roos

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