[openstack-dev] [nova] Questions on pep8 F811 hacking check for microversion

Alex Xu soulxu at gmail.com
Tue Jan 6 13:07:27 UTC 2015

2015-01-06 20:31 GMT+08:00 Jay Pipes <jaypipes at gmail.com>:

> On 01/06/2015 06:25 AM, Chen CH Ji wrote:
>> Based on nova-specs api-microversions.rst
>> we support following function definition format, but it violate the
>> hacking rule pep8 F811 because duplicate function definition
>> we should use #noqa for them , but considering microversion may live for
>> long time ,
>> keep adding #noqa may be a little bit ugly, can anyone suggest a good
>> solution for it ? thanks
>>  >   @api_version(min_version='2.1')
>>  >   def _version_specific_func(self, req, arg1):
>>  >      pass
>>  >
>>  >   @api_version(min_version='2.5')
>>  >   def _version_specific_func(self, req, arg1):
>>  >      pass
> Hey Kevin,
> This was actually one of my reservations about the proposed
> microversioning implementation -- i.e. having functions that are named
> exactly the same, only decorated with the microversioning notation. It
> kinda reminds me of the hell of debugging C++ code that uses STL: how does
> one easily know which method one is in when inside a debugger?
> That said, the only other technique we could try to use would be to not
> use a decorator and instead have a top-level dispatch function that would
> inspect the API microversion (only when the API version makes a difference
> to the output or input of that function) and then dispatch the call to a
> helper method that had the version in its name.
> So, for instance, let's say you are calling the controller's GET
> /$tenant/os-hosts method, which happens to get routed to the
> nova.api.openstack.compute.contrib.hosts.HostController.index() method.
> If you wanted to modify the result of that method and the API microversion
> is at 2.5, you might do something like:
>  def index(self, req):
>      req_api_ver = utils.get_max_requested_api_version(req)
>      if req_api_ver == (2, 5):
>          return self.index_2_5(req)
>      return self.index_2_1(req)
>  def index_2_5(self, req):
>      results = self.index_2_1(req)
>      # Replaces 'host' with 'host_name'
>      for result in results:
>          result['host_name'] = result['host']
>          del result['host']
>      return results
>  def index_2_1(self, req):
>      # Would be a rename of the existing index() method on
>      # the controller....
> Another option would be to use something like JSON-patch to determine the
> difference between two output schemas and automatically translate one to
> another... but that would be a huge effort.

Just JSON-patch only can resolve multiple-version of request/response, we
need handle semantic change also.

But I still think we need something like JSON-patch, it can avoid add new
method only for small request/response changing, like this patch

I have propose before, we can try mapping the request/response into nova
object by json-schema automatically, the nova object will handle the
change. When the request/response changed, nothing will change in REST API
code. I wrote the POC before
This is more easy to maintenance than JSON-patch(thinking about the case of
3.3 patch based on 3.2 patch based on 3.1 patch.....)

> That's the only other way I can think of besides disabling F811, which I
> really would not recommend, since it's a valuable safeguard against
> duplicate function names (especially duplicated test methods).
> Best,
> -jay
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