WriteTopic

class lsst.ts.salobj.topics.WriteTopic(*, salinfo: SalInfo, name: str, sal_prefix: str, min_seq_num: typing.Optional[int] = 1, max_seq_num: int = 2147483647, initial_seq_num: typing.Optional[int] = 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

salinfoSalInfo

SAL component information

namestr

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

sal_prefixstr

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

min_seq_numint or None, optional

Minimum value for the private_seqNum field. The default is 1. If None then private_seqNum is not set; this is needed for the cmdack writer, which sets the field itself.

max_seq_numint, optional

Maximum value for private_seqNum, inclusive. The default is the maximum allowed positive value (private_seqNum is a 4-byte signed int). Ignored if min_seq_num is None.

initial_seq_numint, optional

Initial sequence number; if None use min_seq_num.

Attributes

isopenbool

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.
volatile	Does this topic have volatile durability?

Methods Summary

basic_close()	A synchronous and possibly less thorough version of close.
close()	Shut down and release resources.
put([data])	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.

volatile

Does this topic have volatile durability?

Methods Documentation

basic_close() → None

A synchronous and possibly less thorough version of close.

Intended for exit handlers and constructor error handlers.

async close() → None

Shut down and release resources.

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

put(data: Optional[lsst.ts.salobj.type_hints.BaseDdsDataType] = None) → None

Output this topic.

Parameters

dataself.DataType or None

New message data to replace self.data, if any.

Raises

TypeError

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

set(**kwargs: Any) → bool

Set one or more fields of message data cache self.data.

Parameters

**kwargsdict [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_changebool

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.