Reading and Writing Messages#

Notifier#

The Notifier object is used as a message distributor for a bus. Notifier creates a thread to read messages from the bus and distributes them to listeners.

class can.Notifier(bus, listeners, timeout=1.0, loop=None)[source]#

Manages the distribution of Message instances to listeners.

Supports multiple buses and listeners.

Note

Remember to call stop() after all messages are received as many listeners carry out flush operations to persist data.

Parameters

bus (Union[can.bus.BusABC, List[can.bus.BusABC]]) – A Bus or a list of buses to listen to.
listeners (Iterable[Union[can.listener.Listener, Callable[[can.message.Message], Optional[Awaitable[None]]]]]) – An iterable of Listener or callables that receive a Message and return nothing.
timeout (float) – An optional maximum number of seconds to wait for any Message.
loop (Optional[asyncio.events.AbstractEventLoop]) – An asyncio event loop to schedule the listeners in.

Return type

None

add_bus(bus)[source]#

Add a bus for notification.

Parameters: bus (can.bus.BusABC) – CAN bus instance.
Return type: None

add_listener(listener)[source]#

Add new Listener to the notification list. If it is already present, it will be called two times each time a message arrives.

Parameters: listener (Union[can.listener.Listener, Callable[[can.message.Message], Optional[Awaitable[None]]]]) – Listener to be added to the list to be notified
Return type: None

exception: Optional[Exception]#: Exception raised in thread

remove_listener(listener)[source]#

Remove a listener from the notification list. This method throws an exception if the given listener is not part of the stored listeners.

Parameters: listener (Union[can.listener.Listener, Callable[[can.message.Message], Optional[Awaitable[None]]]]) – Listener to be removed from the list to be notified
Raises: ValueError – if listener was never added to this notifier
Return type: None

stop(timeout=5)[source]#

Stop notifying Listeners when new Message objects arrive and call stop() on each Listener.

Parameters: timeout (float) – Max time in seconds to wait for receive threads to finish. Should be longer than timeout given at instantiation.
Return type: None

Listener#

The Listener class is an “abstract” base class for any objects which wish to register to receive notifications of new messages on the bus. A Listener can be used in two ways; the default is to call the Listener with a new message, or by calling the method on_message_received.

Listeners are registered with Notifier object(s) which ensure they are notified whenever a new message is received.

#!/usr/bin/env python3
import time
import can


def main():

    with can.Bus(receive_own_messages=True) as bus:
        print_listener = can.Printer()
        can.Notifier(bus, [print_listener])

        bus.send(can.Message(arbitration_id=1, is_extended_id=True))
        bus.send(can.Message(arbitration_id=2, is_extended_id=True))
        bus.send(can.Message(arbitration_id=1, is_extended_id=False))

        time.sleep(1.0)


if __name__ == "__main__":
    main()

Subclasses of Listener that do not override on_message_received will cause NotImplementedError to be thrown when a message is received on the CAN bus.

class can.Listener(*args, **kwargs)[source]#

The basic listener that can be called directly to handle some CAN message:

listener = SomeListener()
msg = my_bus.recv()

# now either call
listener(msg)
# or
listener.on_message_received(msg)

# Important to ensure all outputs are flushed
listener.stop()

Parameters

args (Any) –
kwargs (Any) –

Return type

None

on_error(exc)[source]#

This method is called to handle any exception in the receive thread.

Parameters: exc (Exception) – The exception causing the thread to stop
Return type: None

abstract on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

stop()[source]#

Stop handling new messages, carry out any final tasks to ensure data is persisted and cleanup any open resources.

Concrete implementations override.

Return type: None

There are some listeners that already ship together with python-can and are listed below. Some of them allow messages to be written to files, and the corresponding file readers are also documented here.

Note

Please note that writing and the reading a message might not always yield a completely unchanged message again, since some properties are not (yet) supported by some file formats.

Note

Additional file formats for both reading/writing log files can be added via a plugin reader/writer. An external package can register a new reader by using the can.io.message_reader entry point. Similarly, a writer can be added using the can.io.message_writer entry point.

The format of the entry point is reader_name=module:classname where classname is a can.io.generic.BaseIOHandler concrete implementation.

entry_points={
    'can.io.message_reader': [
       '.asc = my_package.io.asc:ASCReader'
   ]
},

BufferedReader#

class can.BufferedReader(*args, **kwargs)[source]#

A BufferedReader is a subclass of Listener which implements a message buffer: that is, when the can.BufferedReader instance is notified of a new message it pushes it into a queue of messages waiting to be serviced. The messages can then be fetched with get_message().

Putting in messages after stop() has been called will raise an exception, see on_message_received().

Attr is_stopped

True if the reader has been stopped

Parameters

args (Any) –
kwargs (Any) –

Return type

None

get_message(timeout=0.5)[source]#

Attempts to retrieve the message that has been in the queue for the longest amount of time (FIFO). If no message is available, it blocks for given timeout or until a message is received (whichever is shorter), or else returns None. This method does not block after can.BufferedReader.stop() has been called.

Parameters: timeout (float) – The number of seconds to wait for a new message.
Returns: the received can.Message or None, if the queue is empty.
Return type: Optional[can.message.Message]

on_message_received(msg)[source]#

Append a message to the buffer.

Raises: BufferError if the reader has already been stopped
Parameters: msg (can.message.Message) –
Return type: None

stop()[source]#

Prohibits any more additions to this reader.

Return type: None

class can.AsyncBufferedReader(*args, **kwargs)[source]#

A message buffer for use with asyncio.

See Asyncio support for how to use with can.Notifier.

Can also be used as an asynchronous iterator:

async for msg in reader:
    print(msg)

Parameters

args (Any) –
kwargs (Any) –

Return type

None

async get_message()[source]#

Retrieve the latest message when awaited for:

msg = await reader.get_message()

Returns: The CAN message.
Return type: can.message.Message

on_message_received(msg)[source]#

Append a message to the buffer.

Must only be called inside an event loop!

Parameters: msg (can.message.Message) –
Return type: None

RedirectReader#

class can.RedirectReader(bus, *args, **kwargs)[source]#

A RedirectReader sends all received messages to another Bus.

Parameters

bus (can.bus.BusABC) –
args (Any) –
kwargs (Any) –

Return type

None

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

Logger#

The can.Logger uses the following can.Listener types to create log files with different file types of the messages received.

class can.Logger(filename, *args, **kwargs)[source]#

Logs CAN messages to a file.

The format is determined from the file suffix which can be one of:

.asc: can.ASCWriter
.blf can.BLFWriter
.csv: can.CSVWriter
.db: can.SqliteWriter
.log can.CanutilsLogWriter
.trc can.TRCWriter
.txt can.Printer

Any of these formats can be used with gzip compression by appending the suffix .gz (e.g. filename.asc.gz). However, third-party tools might not be able to read these files.

The filename may also be None, to fall back to can.Printer.

The log files may be incomplete until stop() is called due to buffering.

Note

This class itself is just a dispatcher, and any positional and keyword arguments are passed on to the returned instance.

Parameters

file – a path-like object to open a file, a file-like object to be used as a file or None to not use a file at all
mode – the mode that should be used to open the file, see open(), ignored if file is None
filename (Optional[Union[str, os.PathLike[str]]]) –
args (Any) –
kwargs (Any) –

Return type

can.io.generic.MessageWriter

static compress(filename, *args, **kwargs)[source]#

Return the suffix and io object of the decompressed file. File will automatically recompress upon close.

Parameters

filename (Union[str, os.PathLike[str]]) –
args (Any) –
kwargs (Any) –

Return type

Tuple[str, Union[TextIO, BinaryIO, gzip.GzipFile]]

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

class can.io.BaseRotatingLogger(*args, **kwargs)[source]#

Base class for rotating CAN loggers. This class is not meant to be instantiated directly. Subclasses must implement the should_rollover() and do_rollover() methods according to their rotation strategy.

The rotation behavior can be further customized by the user by setting the namer and rotator attributes after instantiating the subclass.

These attributes as well as the methods rotation_filename() and rotate() and the corresponding docstrings are carried over from the python builtin BaseRotatingHandler.

Subclasses must set the _writer attribute upon initialization.

Parameters

file – a path-like object to open a file, a file-like object to be used as a file or None to not use a file at all
mode – the mode that should be used to open the file, see open(), ignored if file is None
args (Any) –
kwargs (Any) –

Return type

None

abstract do_rollover()[source]#

Perform rollover.

Return type: None

namer: Optional[Callable[[Union[str, os.PathLike[str]]], Union[str, os.PathLike[str]]]] = None#: If this attribute is set to a callable, the rotation_filename() method delegates to this callable. The parameters passed to the callable are those passed to rotation_filename().

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

rollover_count: int = 0#: An integer counter to track the number of rollovers.

rotate(source, dest)[source]#

When rotating, rotate the current log.

The default implementation calls the rotator attribute of the handler, if it’s callable, passing the source and dest arguments to it. If the attribute isn’t callable (the default is None), the source is simply renamed to the destination.

Parameters

source (Union[str, os.PathLike[str]]) – The source filename. This is normally the base filename, e.g. “test.log”
dest (Union[str, os.PathLike[str]]) – The destination filename. This is normally what the source is rotated to, e.g. “test_#001.log”.

Return type

None

rotation_filename(default_name)[source]#

Modify the filename of a log file when rotating.

This is provided so that a custom filename can be provided. The default implementation calls the namer attribute of the handler, if it’s callable, passing the default name to it. If the attribute isn’t callable (the default is None), the name is returned unchanged.

Parameters: default_name (Union[str, os.PathLike[str]]) – The default name for the log file.
Return type: Union[str, os.PathLike[str]]

rotator: Optional[Callable[[Union[str, os.PathLike[str]], Union[str, os.PathLike[str]]], None]] = None#: If this attribute is set to a callable, the rotate() method delegates to this callable. The parameters passed to the callable are those passed to rotate().

abstract should_rollover(msg)[source]#

Determine if the rollover conditions are met.

Parameters: msg (can.message.Message) –
Return type: bool

stop()[source]#

Stop handling new messages.

Carry out any final tasks to ensure data is persisted and cleanup any open resources.

Return type: None

property writer: can.io.generic.FileIOMessageWriter#: This attribute holds an instance of a writer class which manages the actual file IO.

class can.SizedRotatingLogger(base_filename, max_bytes=0, *args, **kwargs)[source]#

Log CAN messages to a sequence of files with a given maximum size.

The logger creates a log file with the given base_filename. When the size threshold is reached the current log file is closed and renamed by adding a timestamp and the rollover count. A new log file is then created and written to.

This behavior can be customized by setting the namer and rotator attribute.

Example:

from can import Notifier, SizedRotatingLogger
from can.interfaces.vector import VectorBus

bus = VectorBus(channel=[0], app_name="CANape", fd=True)

logger = SizedRotatingLogger(
    base_filename="my_logfile.asc",
    max_bytes=5 * 1024 ** 2,  # =5MB
)
logger.rollover_count = 23  # start counter at 23

notifier = Notifier(bus=bus, listeners=[logger])

The SizedRotatingLogger currently supports the formats

.asc: can.ASCWriter
.blf can.BLFWriter
.csv: can.CSVWriter
.log can.CanutilsLogWriter
.txt can.Printer (if pointing to a file)

Note

The can.SqliteWriter is not supported yet.

The log files on disk may be incomplete due to buffering until stop() is called.

Parameters

base_filename (Union[str, os.PathLike[str]]) – A path-like object for the base filename. The log file format is defined by the suffix of base_filename.
max_bytes (int) – The size threshold at which a new log file shall be created. If set to 0, no rollover will be performed.
args (Any) –
kwargs (Any) –

Return type

None

do_rollover()[source]#

Perform rollover.

Return type: None

should_rollover(msg)[source]#

Determine if the rollover conditions are met.

Parameters: msg (can.message.Message) –
Return type: bool

Printer#

class can.Printer(file=None, append=False, *args, **kwargs)[source]#

The Printer class is a subclass of Listener which simply prints any messages it receives to the terminal (stdout). A message is turned into a string using __str__().

Attr write_to_file

True if this instance prints to a file instead of standard out

Parameters

file (Optional[TextIO]) – An optional path-like object or a file-like object to “print” to instead of writing to standard out (stdout). If this is a file-like object, is has to be opened in text write mode, not binary write mode.
append (bool) – If set to True messages, are appended to the file, else the file is truncated
args (Any) –
kwargs (Any) –

Return type

None

file_size()[source]#

Return an estimate of the current file size in bytes.

Return type: int

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

CSVWriter#

class can.CSVWriter(file, append=False, *args, **kwargs)[source]#

Writes a comma separated text file with a line for each message. Includes a header line.

The columns are as follows:

name of column	format description	example
timestamp	decimal float	1483389946.197
arbitration_id	hex	0x00dadada
extended	1 == True, 0 == False	1
remote	1 == True, 0 == False	0
error	1 == True, 0 == False	0
dlc	int	6
data	base64 encoded	WzQyLCA5XQ==

Each line is terminated with a platform specific line separator.

Parameters

file (TextIO) – a path-like object or a file-like object to write to. If this is a file-like object, is has to open in text write mode, not binary write mode.
append (bool) – if set to True messages are appended to the file and no header line is written, else the file is truncated and starts with a newly written header line
args (Any) –
kwargs (Any) –

Return type

None

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

class can.CSVReader(file, *args, **kwargs)[source]#

Iterator over CAN messages from a .csv file that was generated by CSVWriter or that uses the same format as described there. Assumes that there is a header and thus skips the first line.

Any line separator is accepted.

Parameters

file (TextIO) – a path-like object or as file-like object to read from If this is a file-like object, is has to opened in text read mode, not binary read mode.
args (Any) –
kwargs (Any) –

Return type

None

SqliteWriter#

class can.SqliteWriter(file, table_name='messages', *args, **kwargs)[source]#

Logs received CAN data to a simple SQL database.

The sqlite database may already exist, otherwise it will be created when the first message arrives.

Messages are internally buffered and written to the SQL file in a background thread. Ensures that all messages that are added before calling stop() are actually written to the database after that call returns. Thus, calling stop() may take a while.

Attr str table_name

the name of the database table used for storing the messages

Attr int num_frames

the number of frames actually written to the database, this excludes messages that are still buffered

Attr float last_write

the last time a message war actually written to the database, as given by time.time()

Parameters

file (Optional[Union[TextIO, BinaryIO, gzip.GzipFile]]) –
table_name (str) –
args (Any) –
kwargs (Any) –

Return type

None

Note

When the listener’s stop() method is called the thread writing to the database will continue to receive and internally buffer messages if they continue to arrive before the GET_MESSAGE_TIMEOUT.

If the GET_MESSAGE_TIMEOUT expires before a message is received, the internal buffer is written out to the database file.

However if the bus is still saturated with messages, the Listener will continue receiving until the MAX_TIME_BETWEEN_WRITES timeout is reached or more than MAX_BUFFER_SIZE_BEFORE_WRITES messages are buffered.

Note

The database schema is given in the documentation of the loggers.

Parameters

file (Optional[Union[TextIO, BinaryIO, gzip.GzipFile]]) – a str or path like object that points to the database file to use
table_name (str) – the name of the table to store messages in
args (Any) –
kwargs (Any) –

Return type

None

Warning

In contrary to all other readers/writers the Sqlite handlers do not accept file-like objects as the file parameter.

GET_MESSAGE_TIMEOUT = 0.25#: Number of seconds to wait for messages from internal queue

MAX_BUFFER_SIZE_BEFORE_WRITES = 500#: Maximum number of messages to buffer before writing to the database

MAX_TIME_BETWEEN_WRITES = 5.0#: Maximum number of seconds to wait between writes to the database

stop()[source]#: Stops the reader an writes all remaining messages to the database. Thus, this might take a while and block.

class can.SqliteReader(file, table_name='messages', *args, **kwargs)[source]#

Reads recorded CAN messages from a simple SQL database.

This class can be iterated over or used to fetch all messages in the database with read_all().

Calling len() on this object might not run in constant time.

Attr str table_name

the name of the database table used for storing the messages

Parameters

file (Optional[Union[TextIO, BinaryIO, gzip.GzipFile]]) –
table_name (str) –
args (Any) –
kwargs (Any) –

Return type

None

Note

The database schema is given in the documentation of the loggers.

Parameters

file (Optional[Union[TextIO, BinaryIO, gzip.GzipFile]]) – a str path like object that points to the database file to use
table_name (str) – the name of the table to look for the messages
args (Any) –
kwargs (Any) –

Return type

None

Warning

In contrary to all other readers/writers the Sqlite handlers do not accept file-like objects as the file parameter. It also runs in append=True mode all the time.

read_all()[source]#

Fetches all messages in the database.

Return type: Generator[can.Message]

stop()[source]#: Closes the connection to the database.

Database table format#

The messages are written to the table messages in the sqlite database by default. The table is created if it does not already exist.

The entries are as follows:

Name	Data type	Note
ts	REAL	The timestamp of the message
arbitration_id	INTEGER	The arbitration id, might use the extended format
extended	INTEGER	`1` if the arbitration id uses the extended format, else `0`
remote	INTEGER	`1` if the message is a remote frame, else `0`
error	INTEGER	`1` if the message is an error frame, else `0`
dlc	INTEGER	The data length code (DLC)
data	BLOB	The content of the message

ASC (.asc Logging format)#

ASCWriter logs CAN data to an ASCII log file compatible with other CAN tools such as Vector CANalyzer/CANoe and other. Since no official specification exists for the format, it has been reverse- engineered from existing log files. One description of the format can be found here.

Note

Channels will be converted to integers.

class can.ASCWriter(file, channel=1, *args, **kwargs)[source]#

Logs CAN data to an ASCII log file (.asc).

The measurement starts with the timestamp of the first registered message. If a message has a timestamp smaller than the previous one or None, it gets assigned the timestamp that was written for the last message. It the first message does not have a timestamp, it is set to zero.

Parameters

file (TextIO) – a path-like object or as file-like object to write to If this is a file-like object, is has to opened in text write mode, not binary write mode.
channel (int) – a default channel to use when the message does not have a channel set
args (Any) –
kwargs (Any) –

Return type

None

log_event(message, timestamp=None)[source]#

Add a message to the log file.

Parameters

message (str) – an arbitrary message
timestamp (Optional[float]) – the absolute timestamp of the event

Return type

None

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

stop()[source]#

Closes the underlying file-like object and flushes it, if it was opened in write mode.

Return type: None

ASCReader reads CAN data from ASCII log files .asc, as further references can-utils can be used: asc2log, log2asc.

class can.ASCReader(file, base='hex', relative_timestamp=True, *args, **kwargs)[source]#

Iterator of CAN messages from a ASC logging file. Meta data (comments, bus statistics, J1939 Transport Protocol messages) is ignored.

Parameters

file (TextIO) – a path-like object or as file-like object to read from If this is a file-like object, is has to opened in text read mode, not binary read mode.
base (str) – Select the base(hex or dec) of id and data. If the header of the asc file contains base information, this value will be overwritten. Default “hex”.
relative_timestamp (bool) – Select whether the timestamps are relative (starting at 0.0) or absolute (starting at the system time). Default True = relative.
args (Any) –
kwargs (Any) –

Return type

None

Log (.log can-utils Logging format)#

CanutilsLogWriter logs CAN data to an ASCII log file compatible with can-utils <https://github.com/linux-can/can-utils> As specification following references can-utils can be used: asc2log, log2asc.

class can.CanutilsLogWriter(file, channel='vcan0', append=False, *args, **kwargs)[source]#

Logs CAN data to an ASCII log file (.log). This class is is compatible with “candump -L”.

If a message has a timestamp smaller than the previous one (or 0 or None), it gets assigned the timestamp that was written for the last message. It the first message does not have a timestamp, it is set to zero.

Parameters

file (Union[TextIO, BinaryIO, gzip.GzipFile]) – a path-like object or as file-like object to write to If this is a file-like object, is has to opened in text write mode, not binary write mode.
channel (str) – a default channel to use when the message does not have a channel set
append (bool) – if set to True messages are appended to the file, else the file is truncated
args (Any) –
kwargs (Any) –

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg – the delivered message

CanutilsLogReader reads CAN data from ASCII log files .log

class can.CanutilsLogReader(file, *args, **kwargs)[source]#

Iterator over CAN messages from a .log Logging File (candump -L).

Note

.log-format looks for example like this:

(0.0) vcan0 001#8d00100100820100

Parameters

file (TextIO) – a path-like object or as file-like object to read from If this is a file-like object, is has to opened in text read mode, not binary read mode.
args (Any) –
kwargs (Any) –

Return type

None

BLF (Binary Logging Format)#

Implements support for BLF (Binary Logging Format) which is a proprietary CAN log format from Vector Informatik GmbH.

The data is stored in a compressed format which makes it very compact.

Note

Channels will be converted to integers.

class can.BLFWriter(file, append=False, channel=1, compression_level=- 1, *args, **kwargs)[source]#

Logs CAN data to a Binary Logging File compatible with Vector’s tools.

Parameters

file (BinaryIO) – a path-like object or as file-like object to write to If this is a file-like object, is has to opened in mode “wb+”.
channel (int) – Default channel to log as if not specified by the interface.
append (bool) – Append messages to an existing log file.
compression_level (int) – An integer from 0 to 9 or -1 controlling the level of compression. 1 (Z_BEST_SPEED) is fastest and produces the least compression. 9 (Z_BEST_COMPRESSION) is slowest and produces the most. 0 means that data will be stored without processing. The default value is -1 (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default compromise between speed and compression (currently equivalent to level 6).
args (Any) –
kwargs (Any) –

Return type

None

application_id = 5#: Application identifier for the log writer

file_size()[source]#

Return an estimate of the current file size in bytes.

Return type: int

log_event(text, timestamp=None)[source]#

Add an arbitrary message to the log file as a global marker.

Parameters

text (str) – The group name of the marker.
timestamp (float) – Absolute timestamp in Unix timestamp format. If not given, the marker will be placed along the last message.

max_container_size = 131072#: Max log container size of uncompressed data

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg – the delivered message

stop()[source]#: Stops logging and closes the file.

The following class can be used to read messages from BLF file:

class can.BLFReader(file, *args, **kwargs)[source]#

Iterator of CAN messages from a Binary Logging File.

Only CAN messages and error frames are supported. Other object types are silently ignored.

Parameters

file (BinaryIO) – a path-like object or as file-like object to read from If this is a file-like object, is has to opened in binary read mode, not text read mode.
args (Any) –
kwargs (Any) –

Return type

None

TRC#

Implements basic support for the TRC file format.

Note

Comments and contributions are welcome on what file versions might be relevant.

class can.TRCWriter(file, channel=1)[source]#

Logs CAN data to text file (.trc).

The measurement starts with the timestamp of the first registered message. If a message has a timestamp smaller than the previous one or None, it gets assigned the timestamp that was written for the last message. If the first message does not have a timestamp, it is set to zero.

Parameters

file (TextIO) – a path-like object or as file-like object to write to If this is a file-like object, is has to opened in text write mode, not binary write mode.
channel (int) – a default channel to use when the message does not have a channel set

Return type

None

on_message_received(msg)[source]#

This method is called to handle the given message.

Parameters: msg (can.message.Message) – the delivered message
Return type: None

The following class can be used to read messages from TRC file:

class can.TRCReader(file)[source]#

Iterator of CAN messages from a TRC logging file.

Parameters: file (TextIO) – a path-like object or as file-like object to read from If this is a file-like object, is has to opened in text read mode, not binary read mode.
Return type: None