pytango hlapi device server does not start

[andygotz]

I have installed the latest version of PyTango (from PyPi) 9.2.0 (well done on doing a great job - the installation worked like a charm!). But then when I tried to run a device server which uses the HLAPI. I tried one generated with the latest version of pogo and the PowerSupplyDS in the Getting Started. Both of them fail with this error:

~/tango/classes/pypowersupply$ python3 PowerSupplyDS.py test Exiting: Server exited with unforseen exception: When giving a single class, it must implement HLAPI (see tango.server) terminate called after throwing an instance of 'omni_thread_fatal' Aborted (core dumped)

I can run PyTango device servers which use the low level api. It would be nice if I could use the high level api. The servers are much more compact and easier to write!

Thanks for your help in advance

Andy

[vxgmichel]

The problem here is that the device is not compatible with python 3, because the metaclass is not set properly. Simply replace your class definition with one of the following:

• syntax for python 2:

  class PowerSupply(Device):
      __metaclass__ = DeviceMeta
      [...]

• syntax for python 3:

  class PowerSupply(Device, metaclass=DeviceMeta):
      [...]

• syntax for both, using six:

  @six.add_metaclass(DeviceMeta)
  class PowerSupply(Device):
      [...]

I agree this issue is confusing, and we should do something in pytango to raise a meaningful exception and document it properly. We might also want to update the pogo templates.

[andygotz]

Cool it works! Thanks for the explanation.

[vxgmichel]

Related: metaclass definition won't be necessary anymore after PR #90 is merged.

[andygotz]

Great!