caproto.ChannelData

class caproto.ChannelData(*, alarm=None, value=None, timestamp=None, max_length=None, string_encoding='latin-1', reported_record_type='caproto', max_subscription_backlog: int = 1000)

Base class holding data and metadata which can be sent across a Channel.

Parameters:

value

Data which has to match with this class’s data_type.

timestampfloat, TimeStamp, or 2-tuple, optional

Timestamp associated with the value. Defaults to time.time(). Raw EPICS timestamps are also supported in the form of TimeStamp or (seconds_since_epoch, nanoseconds).

max_lengthint, optional

Maximum array length of the data.

string_encodingstr, optional

Encoding to use for strings, used when serializing and deserializing data.

reported_record_typestr, optional

Though this is not a record, the channel access protocol supports querying the record type. This can be set to mimic an actual record or be set to something arbitrary. Defaults to ‘caproto’.

Methods

auth_read(hostname, username, data_type, *)	Get DBR data and native data, converted to a specific type
auth_write(hostname, username, data, ...[, ...])	Data write hook for clients.
calculate_length(value)	Calculate the number of elements given a value
check_access(hostname, username)	This always returns AccessRights.READ|AccessRights.WRITE.
is_compatible_array(value)	Check if the provided value is a compatible array.
post_state_change(state, new_value)	This is called by the server when it exits its StateUpdateContext.
pre_state_change(state, new_value)	This is called by the server when it enters its StateUpdateContext.
preprocess_value(value)	Pre-process values destined for verify_value and write
publish(flags)	Publish data to appropriate queues matching the SubscriptionSpec.
read(data_type)	Read out the ChannelData as data_type.
subscribe(queue, sub_spec, sub)	Subscribe a queue for the given subscription specification.
unsubscribe(queue, sub_spec)	Unsubscribe a queue for the given subscription specification.
update_fields(value)	This is a hook for subclasses to update field instance data.
verify_value(data)	Verify a value prior to it being written by CA or Python
write(value, *[, flags, verify_value, ...])	Write data from native Python types.
write_from_dbr(data, data_type, metadata, *)	Write data from a provided DBR data type.
write_metadata([publish, units, precision, ...])	Write metadata, optionally publishing information to clients.

Attributes

alarm	The ChannelAlarm associated with this data
data_type
default_value
epics_timestamp	EPICS timestamp as (seconds, nanoseconds) since EPICS epoch.
length	The number of elements (length) of the current value
max_length	The maximum number of elements (length) this channel can hold
severity	Alarm severity
status	Alarm status
timestamp	UNIX timestamp in seconds.
value	Read-only access to value data
max_subscription_backlog