[Python-ideas] Redefining method

[Kyle Lahnakoski]

I think C# calls methods that are added to a class "extension methods".
You can make a decorator that will do that for you:

> def extend(cls):
>     """
>     DECORATOR TO ADD METHODS TO CLASSES
>     :param cls: THE CLASS TO ADD THE METHOD TO
>     :return:
>     """
>     def extender(func):
>         setattr(cls, get_function_name(func), func)
>         return func
>     return extender

and use it

> C = MyClass
> @extend(C)
> def foo(self, schesome_param):
>     some_code()



On 2018-07-30 14:12, Chris Barker via Python-ideas wrote:
> On Mon, Jul 30, 2018 at 9:10 AM, Nick Coghlan <ncoghlan at gmail.com
> <mailto:ncoghlan at gmail.com>> wrote:
>
>     If you need to replace them for some reason, it will preferably be
>     within a temporary bounded scope, using a tool like
>     unittest.mock.patch, rather than as a permanent change that affects
>     every other use of the class within the process.
>
>
>  yup -- but you can still do a raw monkey-patch anyway. You asked for:
>
>     > Thank you for your question. You asked why not
>     >> c = MyClass
>     >> o = c()
>     >>
>     >> def c.foo(cls): ...
>
>
> do you mean this? you want a classmethod? or is this what you mean? --
> which you can do:
>
> C = MyClass
>
> def foo(self, some_param):
>     some_code()
>
> C.foo = foo
>
> (note that I used a capital C -- capitalized names are traditional for
> classes -- see PEP 8)
>
> In that case, any existing, and new instances of the C class will now
> have the foo method.
>
> Also -- that line: C = MyClass -- binds the name "C" to the very same
> class object as MyClass -- so you will have just monkey=patched
> MyClass -- I"m guessing you didn't want that. If not, and you wanted C
> t be a copy of MyClass that you could then change/add/remove methods
> from, then you want subclassing -- that is exactly what it is for.
>
> Then there is this:
>  
>
>     >> def o.bar(self): ...
>
>
> which is monkey patching an instance object, which you can also do,
> but you don't get a bound method -- i.e. it doesn't get self passed in
> automatically.
>
> -CHB
>
>
>
>
>
>
>
>
>
>  
>
>     > I've the same same query, but never had the courage to ask. So that
>     > you for asking. And also giving me a chance to share my thoughts.
>
>     It's essentially due to the fact that while we deliberately allow
>     runtime monkeypatching (as it's sometimes the best available answer),
>     we also strongly encourage the idea of treating it as a last resort
>     option (outside specific use cases like testing).
>
>     So if you want to define methods on a class, the strongly preferred
>     place to define them is inside the class definition, where they're
>     easy for future maintainers of that class to find.
>
>
>     Cheers,
>     Nick.
>
>     P.S. While it's *not* explicitly part of Python's design rationale,
>     http://connascence.io/locality.html
>     <http://connascence.io/locality.html> and the rest of that site
>     provide
>     some good info on the kinds of problems that "action at a distance"
>     effects, like monkeypatching class definitions, can cause in a code
>     base.
>
>     -- 
>     Nick Coghlan   |   ncoghlan at gmail.com <mailto:ncoghlan at gmail.com> 
>      |   Brisbane, Australia
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>
>
>
> -- 
>
> Christopher Barker, Ph.D.
> Oceanographer
>
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