cloudstack-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Will Stevens <williamstev...@gmail.com>
Subject Re: Python Question (with regards to Marvin)
Date Sun, 01 May 2016 00:05:43 GMT
That's strange. That means the @classmethod decorator is not working. You
should have gotten the instance method in both cases.

What if you don't instantiate Test and only do the following.

Test.run()

In both cases.
On Apr 30, 2016 6:04 PM, "Tutkowski, Mike" <Mike.Tutkowski@netapp.com>
wrote:

> I ran this with an online Python tool and it calls the class method:
>
> 1       class Test:
> 2         def run(self):
> 3             print 'instance hi'
> 4
> 5         @classmethod
> 6         def run(cls):
> 7             print 'class hi'
> 8
> 9       test = Test()
> 10
> 11      test.run()
>
> If I reverse the order of the methods, the instance method is invoked:
>
> 1       class Test:
> 2         @classmethod
> 3         def run(cls):
> 4             print 'class hi'
> 5
> 6         def run(self):
> 7             print 'instance hi'
> 8
> 9       test = Test()
> 10
> 11      test.run()
>
> As I suspected, I think this means we have a problem in base.py.
> ________________________________________
> From: Will Stevens <williamstevens@gmail.com>
> Sent: Saturday, April 30, 2016 1:46 PM
> To: dev@cloudstack.apache.org
> Subject: Re: Python Question (with regards to Marvin)
>
> I am on my phone so I have not been able to research this for you. I think
> you are right for the most part.  Instead of multiple methods, python kind
> of fakes overloading by being to have named function arguments which can
> have default values, so you can call the method with a dynamic number of
> arguments making it appear like you are overloading, but you are actually
> calling the same function.
>
> I think in this case the two methods are actually in different scopes (even
> though they are next to each other).  The decorator actually wraps the
> method, so I believe in the actual runtime the to methods are in different
> scopes.
>
> I would have to look into this more to know for sure. I am taking a few
> minute break from building garden boxes right now. :)
> On Apr 30, 2016 3:31 PM, "Tutkowski, Mike" <Mike.Tutkowski@netapp.com>
> wrote:
>
> > Will - You can override a method in Python, but can you overload it?
> >
> >
> >
> http://stackoverflow.com/questions/10202938/how-do-i-use-method-overloading-in-python
> >
> > > On Apr 30, 2016, at 6:23 AM, Will Stevens <williamstevens@gmail.com>
> > wrote:
> > >
> > > Here is a pretty good explanation.
> > >
> > >
> >
> http://stackoverflow.com/questions/136097/what-is-the-difference-between-staticmethod-and-classmethod-in-python
> > >
> > > I am guessing that both exist because the function is called both with
> a
> > > host instance and with the class itself.
> > >
> > > Class instance example: `h.enableMaintenance(client)`
> > >
> > > Class example: `Host.enableMaintenance(client, 1)`
> > >
> > > In both cases the first parameter is implicitly `h` and `Host`
> > > respectively.
> > >
> > > I am not sure why we need both (because I am not familiar with how this
> > > code is called), but method overloading is definitely valid in python.
> > >
> > > On Apr 30, 2016 1:08 AM, "Tutkowski, Mike" <Mike.Tutkowski@netapp.com>
> > > wrote:
> > >>
> > >> Hi everyone,
> > >>
> > >>
> > >> I received an error when trying to invoke the instance version of
> > > enableMaintenance (below).
> > >>
> > >>
> > >> 'TypeError: enableMaintenance() takes exactly 3 arguments (2
> given)\n']
> > >>
> > >>
> > >> I looked at base.py and it has the following with regards to
> maintenance
> > > mode for hosts:
> > >>
> > >>
> > >>    def enableMaintenance(self, apiclient):
> > >>
> > >>        """enables maintenance mode Host"""
> > >>
> > >>
> > >>        cmd = prepareHostForMaintenance.prepareHostForMaintenanceCmd()
> > >>
> > >>        cmd.id = self.id
> > >>
> > >>        return apiclient.prepareHostForMaintenance(cmd)
> > >>
> > >>
> > >>    @classmethod
> > >>
> > >>    def enableMaintenance(cls, apiclient, id):
> > >>
> > >>        """enables maintenance mode Host"""
> > >>
> > >>
> > >>        cmd = prepareHostForMaintenance.prepareHostForMaintenanceCmd()
> > >>
> > >>        cmd.id = id
> > >>
> > >>        return apiclient.prepareHostForMaintenance(cmd)
> > >>
> > >>
> > >> Now, I definitely have a lot more Java experience than Python, but -
> as
> > > far as I know - having two methods with the same name such as this
> (even
> > if
> > > one is an instance method and the other is a class method) is not
> really
> > > "permitted" in Python.
> > >>
> > >>
> > >> I mean, technically it's permitted, but the second one will override
> the
> > > first one.
> > >>
> > >>
> > >> Can any of our Python people comment on this?
> > >>
> > >>
> > >> I was thinking I'd remove the class method (assuming my knowledge here
> > > regarding this topic is correct).
> > >>
> > >>
> > >> Thanks!
> > >>
> > >> Mike
> > >>
> > >>
> > >>
> >

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message