WriteTopic

class lsst.ts.salobj.topics.WriteTopic(*, salinfo, name, sal_prefix, min_seq_num=1, max_seq_num=2147483647, initial_seq_num=None)

Bases: lsst.ts.salobj.topics.base_topic.BaseTopic

Base class for topics that are output.

This includes controller events, controller telemetry, remote commands and cmdack writers.

Parameters:

salinfo : SalInfo

SAL component information

name : str

Topic name, without a “command_” or “logevent_” prefix.

sal_prefix : str

SAL topic prefix: one of “command_”, “logevent_” or “”

min_seq_num : int or None

Minimum value for the private_seqNum field. If None then private_seqNum is not set; this is needed for the cmdack writer, which sets the field itself.

max_seq_num : int

Maximum value for private_seqNum, inclusive. Ignored if min_seq_num is None.

initial_seq_num : int (optional)

Initial sequence number; if None use min_seq_num.

Attributes:

isopen : bool

Is this read topic open? True until close is called.

Attributes Summary

DataType	The class of data for this topic.
data	Get or set internally cached data.
has_data	Has data ever been set?
metadata	Get topic metadata as a TopicMetadata, if available, else None.

Methods Summary

close()	Shut down and release resources.
put([data, priority])	Output this topic.
set(**kwargs)	Set one or more fields of self.data.

Attributes Documentation

DataType

The class of data for this topic.

data

Get or set internally cached data.

Parameters:

data : DataType

New data.

Raises:

TypeError

If data is not an instance of DataType

Notes

You must not modify the returned data, nor assume that it will be constant. If you need a copy then make it yourself.

has_data

Has data ever been set?

metadata

Get topic metadata as a TopicMetadata, if available, else None.

Methods Documentation

close()

Shut down and release resources.

Intended to be called by SalInfo.close(), since that tracks all topics.

put(data=None, priority=0)

Output this topic.

Parameters:

data : self.DataType or None

New data to replace self.data, if any.

priority : int (optional)

Priority; used to set the priority field of events. Ignored for commands and telemetry.

Raises:

TypeError

If data is not None and not an instance of DataType.

set(**kwargs)

Set one or more fields of self.data.

Parameters:

**kwargs : dict [str, any]

Dict of field name: new value for that field:

• Any key whose value is None is checked for existence, but the value of the field is not changed.
• If the field being set is an array then the value must either be an array of the same length or a scalar (which replaces every element of the array).

Returns:

did_change : bool

True if data was changed or if this was the first call to set.

Raises:

AttributeError

If the topic does not have the specified field.

ValueError

If the field cannot be set to the specified value.

Notes

If one or more fields cannot be set, the data may be partially updated. This is not ideal, but is pragmatic because it is difficult to copy SAL topics (see TSS-3195).