New attribute decorators

In order to improve with readability and better match Python’s property syntax, the tango.server.attribute decorator has a few new options. No changes are required for existing code. These are the new options:

• @<attribute>.getter

• @<attribute>.read

• @<attribute>.is_allowed

The getter and read methods are aliases for each other and are applicable to reading of attributes. They provide symmetry with the decorators that handle writing to attributes: setter and write. The new is_allowed decorator provides a consistent way to define the “is allowed” method for an attribute.

Unlike Python properties, the names of the decorated methods do not have to match.

A simple example:

from tango import AttReqType, DevState
from tango.server import Device, attribute

class Test(Device):
    _simulated_voltage = 0.0

    voltage = attribute(dtype=float)

    @voltage.getter
    def voltage(self):
        return self._simulated_voltage

    @voltage.setter
    def voltage(self, value):
        self._simulated_voltage = value

    @voltage.is_allowed
    def voltage_can_be_changed(self, req_type):
        if req_type == AttReqType.WRITE_REQ:
            return self.get_state() == DevState.ON
        else:
            return True

There are many variations possible when using these. See more in Writing TANGO servers in Python.