utils

ska.low.mccs.utils.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 ([type]) – [description]

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

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

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

ska.low.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.

Parameters
  • func – the function to call

  • kwargs – parameters to be jsonified and passed to func

Ptype func

callable

Ptype kwargs

any

Returns

the return value of func

Example

Suppose you need to use MccsMaster.Allocate() to command a master device to allocate certain stations and tiles to a subarray. Allocate() accepts a single JSON string argument. Instead of

parameters={“id”: id, “stations”: stations, “tiles”: tiles} json_string=json.dumps(parameters) master.Allocate(json_string)

save yourself the trouble and

call_with_json(master.Allocate,

id=id, stations=stations, tiles=tiles)

class ska.low.mccs.utils.json_input(schema_path=None)[source]

Method decorator that parses and validates JSON input into a python object. The wrapped method is thus called with a JSON string, but can be implemented as if it had been passed an object.

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

Parameters

schema_path – an optional path to a schema against which the JSON should be validated. Not working at the moment, so leave it None.

Ptype

string

Raises
  • FileNotFoundException – if no file is found at the schema path provided

  • json.JSONDecodeError – if the file at the specified schema path is not valid JSON

Example

Conceptually, MccsMaster.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:

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

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