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.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 type (class) for a message of this topic.
`data`	Internally cached message.
`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 message data cache `self.data`.

Attributes Documentation

DataType¶

The type (class) for a message of this topic.

When you read or write a message for this topic you are reading or writing an instance of DataType.

Notes

The preferred way to write a message for a topic is:

RemoteCommand.set_start to start a command.
CommandEvent.set_put to write an event.
CommandTelemetry.set_put to write a telemetry message.

However, it is also possible to use DataType to create a message, then write, it as separate operations. For example, assuming we have a Remote for SAL component “Test”:

# The preferred way to issue a command:
await = remote.cmd_wait.set_put(duration=2, timeout=5)

# But an alternative is to first create the command,
# then send it, as two separate operations:
message = remote.cmd_wait.DataType(duration=2)
await remote.cmd_wait.start(message, timeout=5)

# Or, even more verbosely:
message = remote.cmd_wait.DataType()
message.duration = 2
await remote.cmd_wait.start(message, timeout=5)

data¶

Internally cached message.

Raises:	TypeError If `data` is not an instance of `DataType`

Notes

Do not assume the data will be constant. You can make a copy using copy.copy(data).

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 message 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 message data cache 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 `self.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 message data may be partially updated.

Navigation

WriteTopic¶