channel

Channel information.

Channel dataclass

Channel(name, data_type, sample_rate, time=None, publisher=None, partition_id=None, partition_index=None, expected_latency=None)

Metadata associated with a channel.

Channels have the form {domain}:*.

Parameters:

Name	Type	Description	Default
name	str	The name associated with this channel.	required
data_type	dtype	The data type associated with this channel.	required
sample_rate	float	The sampling rate associated with this channel.	required
time	int	The timestamp when this metadata became active.	None
publisher	str	The publisher associated with this channel.	None
partition_id	str	The partition ID associated with this channel.	None
partition_index	int | None	Partition index for the channel. It is unique within the partition and allows the use of an integer value to identify the channel instead of a string.	None
expected_latency	int | None	Expected publication latency for this channel's data, in seconds.	None

from_field classmethod

from_field(field)

Create a Channel from Arrow Flight field metadata.

Parameters:

Name	Type	Description	Default
field	field	The channel field containing relevant metadata.	required

Returns:

Type	Description
Channel	The newly created channel.

Source code in arrakis/channel.py

@classmethod
def from_field(cls, field: pyarrow.field) -> Channel:
    """Create a Channel from Arrow Flight field metadata.

    Parameters
    ----------
    field : pyarrow.field
        The channel field containing relevant metadata.

    Returns
    -------
    Channel
        The newly created channel.

    """
    data_type = numpy.dtype(_list_dtype_to_str(field.type))
    sample_rate = float(field.metadata[b"rate"].decode())
    return cls(field.name, data_type, sample_rate)

from_json classmethod

from_json(payload)

Create a Channel from its JSON representation.

Parameters:

Name	Type	Description	Default
payload	str	The JSON-serialized channel.	required

Returns:

Type	Description
Channel	The newly created channel.

Source code in arrakis/channel.py

@classmethod
def from_json(cls, payload: str) -> Channel:
    """Create a Channel from its JSON representation.

    Parameters
    ----------
    payload : str
        The JSON-serialized channel.

    Returns
    -------
    Channel
        The newly created channel.

    """
    obj = json.loads(payload)
    obj["data_type"] = numpy.dtype(obj["data_type"])
    return cls(**obj)

to_json

to_json(time=None)

Serialize channel metadata to JSON.

Parameters:

Name	Type	Description	Default
time	int	If specified, the timestamp when this metadata became active.	None

Source code in arrakis/channel.py

def to_json(self, time: int | None = None) -> str:
    """Serialize channel metadata to JSON.

    Parameters
    ----------
    time : int, optional
        If specified, the timestamp when this metadata became active.

    """
    # generate dict from dataclass and adjust fields
    # to be JSON compatible. In addition, store the
    # channel name, as well as updating the timestamp
    # if passed in.
    obj = asdict(self)
    obj["data_type"] = numpy.dtype(self.data_type).name
    if time is not None:
        obj["time"] = time
    obj = {k: v for k, v in obj.items() if v is not None}
    return json.dumps(obj)

ParsedChannelName dataclass

ParsedChannelName(domain, subsystem, subsystem_delimiter, rest)

A parsed channel name

Channel names have the following structure:

<domain>:<subsystem>[-_]<rest>

parse classmethod

parse(name)

Parse a channel name into it's constituent parts

Source code in arrakis/channel.py

@classmethod
def parse(cls, name: str) -> ParsedChannelName:
    """Parse a channel name into it's constituent parts"""
    if rem := CHANNEL_NAME_RE.match(name):
        return cls(
            rem["domain"],
            rem["subsystem"],
            rem["delimiter"],
            rem["rest"],
        )
    msg = "Invalid channel name structure."
    raise ValueError(msg)

PartitionInfo dataclass

PartitionInfo(name, id, index)

Partition metadata associated with a channel.

Parameters:

Name	Type	Description	Default
name	str	The name associated with this channel.	required
id	str	The partition ID associated with this channel.	required
index	int	Partition index for the channel. It is unique within the partition and allows the use of an integer value to identify the channel instead of a string.	required

from_channel classmethod

from_channel(channel)

Extract partition information from a Channel.

Parameters:

Name	Type	Description	Default
channel	Channel	The channel containing relevant metadata.	required

Returns:

Type	Description
PartitionInfo	The newly created partition information.

Source code in arrakis/channel.py

@classmethod
def from_channel(cls, channel: Channel) -> PartitionInfo:
    """Extract partition information from a Channel.

    Parameters
    ----------
    channel : Channel
        The channel containing relevant metadata.

    Returns
    -------
    PartitionInfo
        The newly created partition information.

    """
    assert channel.partition_id is not None
    assert channel.partition_index is not None
    return cls(
        name=channel.name,
        id=channel.partition_id,
        index=channel.partition_index,
    )