Utils module (ska_low_mccs.utils)

Module for MCCS utils.

call_with_json(func, **kwargs)[source]

Allows the calling of a command that accepts a JSON string as input, with the actual unserialised parameters.

For example, suppose you need to use Allocate(resources) command to tell a controller device to allocate certain stations and tiles to a subarray. Allocate accepts a single JSON string argument. Instead of

Example:

parameters={"id": id, "stations": stations, "tiles": tiles}
json_string=json.dumps(parameters)
controller.Allocate(json_string)

save yourself the trouble and

Example:

call_with_json(controller.Allocate, id=id, stations=stations, tiles=tiles)
Parameters
  • func – the function handle to call

  • kwargs – parameters to be jsonified and passed to func

Returns

the return value of func

class json_input(schema_path=None)[source]

Method decorator that parses and validates JSON input into a python dictionary, which is then passed to the method as kwargs. The wrapped method is thus called with a JSON string, but can be implemented as if it had been passed a sequence of named arguments.

If the string cannot be parsed as JSON, an exception is raised.

For example, conceptually, MccsController.Allocate() takes as arguments a subarray id, an array of stations, and an array of tiles. In practice, however, these arguments are encoded into a JSON string. Implement the function with its conceptual parameters, then wrap it in this decorator:

Example:

@json_input
def MccsController.Allocate(id, stations, tiles):

The decorator will provide the JSON interface and handle the decoding for you.

__init__(schema_path=None)[source]

Initialises a callable json_input object, to function as a device method generator.

Parameters

schema_path (typing.Optional[str]) – an optional path to a schema against which the JSON should be validated. Not working at the moment, so leave it None.

tango_raise(msg, reason='API_CommandFailed', severity=tango.ErrSeverity.ERR, _origin=None)[source]

Helper function to provide a concise way to throw tango.Except.throw_exception.

Example:

class MyDevice(Device):
    @command
    def some_command(self):
        if condition:
            pass
        else:
            tango_throw("Condition not true")
Parameters
  • msg (str) – message

  • reason (str) – the tango api tango.DevError description string, defaults to “API_CommandFailed”

  • severity (tango.ErrSeverity) – the tango error severity, defaults to tango.ErrSeverity.ERR

  • _origin (typing.Optional[str]) – the calling object name, defaults to None (autodetected) Note that autodetection only works for class methods not e.g. decorators

Raises

TypeError – if used from an object that is not a tango device instance

Return type

None