[Python-Dev] lament for the demise of unbound methods
Chris Withers
chris at simplistix.co.uk
Thu Jul 4 19:20:54 CEST 2013
On 04/07/2013 18:00, Guido van Rossum wrote:
> Thanks for the code pointers. So it's all about monkeypatching. :-)
Well, that's the testfixtures use case, but for mush it's about figuring
out whether you need to instantiate a class before calling a callable.
MyClass.a_method is a bit like a functools.partial in the mush case, if
I can pass that object around and know what to do with it (which I can
in Python 2) then I only have to pass that around.
In Python3, I either have to pass around the class, the method and a
flag to indicate that a class and method are being passed, or wrap my
own unboundmethod equivalent, meaning mush users would have to write
method(MyClass, 'a_method') under Python 3 when they can just write
MyClass.a_method under Python 2.
> I
> have only a little sympathy, as there still seems to be a way to do
> this, it's just less convenient. Too bad.
I don't know that Victor's suggestion will actually work in all the
cases that MyClass.a_method.im_class does :-S
Chris
> On Thu, Jul 4, 2013 at 9:42 AM, Chris Withers <chris at simplistix.co.uk
>
> Hi Guido,
>
> I've bumped into this a couple of times.
>
> First time was when I wanted to know whether what I had was a
> classmethod, staticmethod or normal method here:
>
> https://github.com/Simplistix/__testfixtures/blob/master/__testfixtures/replace.py#L59
> <https://github.com/Simplistix/testfixtures/blob/master/testfixtures/replace.py#L59>
>
> This resulted in having to trawl through __dict__ here:
>
> https://github.com/Simplistix/__testfixtures/blob/master/__testfixtures/resolve.py#L17
> <https://github.com/Simplistix/testfixtures/blob/master/testfixtures/resolve.py#L17>
>
> ...rather than just using getattr.
>
> I bumped into it again, yesterday, trying to add support for classes
> to this lightweight dependency injection framework I'm developing:
>
> https://github.com/Simplistix/__mush/blob/master/tests/test___runner.py#L189
> <https://github.com/Simplistix/mush/blob/master/tests/test_runner.py#L189>
>
> Here's my local copy of that test:
>
> https://gist.github.com/__cjw296/db64279c69cdc0c5e112
> <https://gist.github.com/cjw296/db64279c69cdc0c5e112>
>
> The workaround I was playing with this morning is a wrapper so that
> I know I have a class method, although what I really want to write
> at this line is:
>
> https://gist.github.com/__cjw296/db64279c69cdc0c5e112#__file-gistfile1-txt-L40
> <https://gist.github.com/cjw296/db64279c69cdc0c5e112#file-gistfile1-txt-L40>
>
> runner = Runner(T0, C1.meth, C2.meth1, C2.meth2)
>
> ...but if I do that, how can the runner know that what it gets for
> its second argument is a class method of C1?
> (which is this case means that it should do C1().meth() rather than
> C1.meth())
>
> cheers,
>
> Chris
>
>
> On 04/07/2013 17:25, Guido van Rossum wrote:
>
> Chris, what do you want to do with the knowledge you are seeking?
>
> --Guido van Rossum (sent from Android phone)
>
> On Jul 4, 2013 4:28 AM, "Chris Withers" <chris at simplistix.co.uk
> <mailto:chris at simplistix.co.uk>
> <mailto:chris at simplistix.co.uk
> <mailto:chris at simplistix.co.uk>__>> wrote:
>
> Hi All,
>
> In Python 2, I can figure out whether I have a method or a
> function,
> and, more importantly, for an unbound method, I can figure
> out what
> class the method belongs to:
>
> >>> class MyClass(object):
> ... def method(self): pass
> ...
> >>> MyClass.method
> <unbound method MyClass.method>
> >>> MyClass.method.im_class
> <class '__main__.MyClass'>
>
> There doesn't appear to be any way in Python 3 to do this,
> which is
> a little surprising and frustrating...
>
> What am I missing here?
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python
> Consulting
> - http://www.simplistix.co.uk
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> --Guido van Rossum (python.org/~guido <http://python.org/~guido>)
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