[Python-Dev] lament for the demise of unbound methods (original) (raw)

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/testrunner.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 >>> MyClass.method.imclass <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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