File IO¶

Reading and Writing Files¶

can.LogReader(filename, **kwargs)[source]¶

Find and return the appropriate MessageReader instance for a given file suffix.

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

.asc can.ASCReader
.blf can.BLFReader
.csv can.CSVReader
.db can.SqliteReader
.log can.CanutilsLogReader
.mf4 can.MF4Reader (optional, depends on asammdf)
.trc can.TRCReader

Gzip compressed files can be used as long as the original files suffix is one of the above (e.g. filename.asc.gz).

Exposes a simple iterator interface, to use simply:

for msg in can.LogReader("some/path/to/my_file.log"):
    print(msg)

Parameters:

filename (str | os.PathLike[str]) – the filename/path of the file to read from
kwargs (Any)

Raises:

ValueError – if the filename’s suffix is of an unknown file type

Return type:

MessageReader

Note

There are no time delays, if you want to reproduce the measured delays between messages look at the can.MessageSync class.

Note

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

can.Logger(filename, **kwargs)[source]¶

Find and return the appropriate MessageWriter instance for a given file suffix.

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
.mf4 can.MF4Writer (optional, depends on asammdf)
.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.

Parameters:

filename (str | PathLike[str] | None) – the filename/path of the file to write to, may be a path-like object or None to instantiate a Printer
kwargs (Any)

Raises:

ValueError – if the filename’s suffix is of an unknown file type

Return type:

MessageWriter

Note

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

can.io.logger.MESSAGE_WRITERS: Final[Dict[str, Type[MessageWriter]]] = {'.asc': <class 'can.io.asc.ASCWriter'>, '.blf': <class 'can.io.blf.BLFWriter'>, '.csv': <class 'can.io.csv.CSVWriter'>, '.db': <class 'can.io.sqlite.SqliteWriter'>, '.log': <class 'can.io.canutils.CanutilsLogWriter'>, '.mf4': <class 'can.io.mf4.MF4Writer'>, '.trc': <class 'can.io.trc.TRCWriter'>, '.txt': <class 'can.io.printer.Printer'>}¶: A map of file suffixes to their corresponding can.io.generic.MessageWriter class

can.io.player.MESSAGE_READERS: Final[Dict[str, Type[MessageReader]]] = {'.asc': <class 'can.io.asc.ASCReader'>, '.blf': <class 'can.io.blf.BLFReader'>, '.csv': <class 'can.io.csv.CSVReader'>, '.db': <class 'can.io.sqlite.SqliteReader'>, '.log': <class 'can.io.canutils.CanutilsLogReader'>, '.mf4': <class 'can.io.mf4.MF4Reader'>, '.trc': <class 'can.io.trc.TRCReader'>}¶: A map of file suffixes to their corresponding can.io.generic.MessageReader class

Printer¶

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

Bases: MessageWriter

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 (TextIO | None) – 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, it 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
kwargs (Any)

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 (Message) – the delivered message
Return type:: None

CSVWriter¶

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

Bases: TextIOMessageWriter

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
kwargs (Any)

on_message_received(msg)[source]¶

This method is called to handle the given message.

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

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

Bases: TextIOMessageReader

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.
kwargs (Any)

SqliteWriter¶

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

Bases: MessageWriter, BufferedReader

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 (TextIO | BinaryIO | GzipFile | None)
table_name (str)
kwargs (Any)

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 (TextIO | BinaryIO | GzipFile | None) – 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
kwargs (Any)

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', **kwargs)[source]¶

Bases: MessageReader

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 (TextIO | BinaryIO | GzipFile | None)
table_name (str)
kwargs (Any)

Note

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

Parameters:

file (TextIO | BinaryIO | GzipFile | None) – 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
kwargs (Any)

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, **kwargs)[source]¶

Bases: TextIOMessageWriter

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
kwargs (Any)

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

Add a message to the log file.

Parameters:

message (str) – an arbitrary message
timestamp (float | None) – 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 (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, **kwargs)[source]¶

Bases: TextIOMessageReader

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.
kwargs (Any)

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, **kwargs)[source]¶

Bases: TextIOMessageWriter

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 (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 (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
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, **kwargs)[source]¶

Bases: TextIOMessageReader

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.
kwargs (Any)

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, **kwargs)[source]¶

Bases: FileIOMessageWriter

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).
kwargs (Any)

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, **kwargs)[source]¶

Bases: BinaryIOMessageReader

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.
kwargs (Any)

MF4 (Measurement Data Format v4)¶

Implements support for MF4 (Measurement Data Format v4) which is a proprietary format from ASAM (Association for Standardization of Automation and Measuring Systems), widely used in many automotive software (Vector CANape, ETAS INCA, dSPACE ControlDesk, etc.).

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

Note

MF4 support has to be installed as an extra with for example pip install python-can[mf4].

Note

Channels will be converted to integers.

Note

MF4Writer does not suppport the append mode.

class can.MF4Writer(file, database=None, compression_level=2, **kwargs)[source]¶

Bases: BinaryIOMessageWriter

Logs CAN data to an ASAM Measurement Data File v4 (.mf4).

MF4Writer does not support append mode.

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 (BinaryIO | GzipFile) – A path-like object or as file-like object to write to. If this is a file-like object, is has to be opened in binary write mode, not text write mode.
database (str | os.PathLike[str] | None) – optional path to a DBC or ARXML file that contains message description.
compression_level (int) – compression option as integer (default 2) * 0 - no compression * 1 - deflate (slower, but produces smaller files) * 2 - transposition + deflate (slowest, but produces the smallest files)
kwargs (Any)

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 (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

The MDF format is very flexible regarding the internal structure and it is used to handle data from multiple sources, not just CAN bus logging. MDF4Writer will always create a fixed internal file structure where there will be three channel groups (for standard, error and remote frames). Using this fixed file structure allows for a simple implementation of MDF4Writer and MF4Reader classes. Therefor MF4Reader can only replay files created with MF4Writer.

The following class can be used to read messages from MF4 file:

class can.MF4Reader(file, **kwargs)[source]¶

Bases: BinaryIOMessageReader

Iterator of CAN messages from a MF4 logging file.

The MF4Reader only supports MF4 files that were recorded with python-can.

Parameters:

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

stop()[source]¶

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

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, **kwargs)[source]¶

Bases: TextIOMessageWriter

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
kwargs (Any)

on_message_received(msg)[source]¶

This method is called to handle the given message.

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

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

class can.TRCReader(file, **kwargs)[source]¶

Bases: TextIOMessageReader

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.
kwargs (Any)

Rotating Loggers¶

class can.io.BaseRotatingLogger(**kwargs)[source]¶

Bases: MessageWriter, ABC

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
kwargs (Any)

abstract do_rollover()[source]¶

Perform rollover.

Return type:: None

namer: Callable[[str | os.PathLike[str]], str | os.PathLike[str]] | None = 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 (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 (str | PathLike[str]) – The source filename. This is normally the base filename, e.g. “test.log”
dest (str | 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 (str | PathLike[str]) – The default name for the log file.
Return type:: str | PathLike[str]

rotator: Callable[[str | os.PathLike[str], str | os.PathLike[str]], None] | 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 (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

abstract property writer: FileIOMessageWriter¶: This attribute holds an instance of a writer class which manages the actual file IO.

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

Bases: BaseRotatingLogger

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 (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.
kwargs (Any)

do_rollover()[source]¶

Perform rollover.

Return type:: None

should_rollover(msg)[source]¶

Determine if the rollover conditions are met.

Parameters:: msg (Message)
Return type:: bool

property writer: FileIOMessageWriter¶: This attribute holds an instance of a writer class which manages the actual file IO.

Replaying Files¶

class can.MessageSync(messages, timestamps=True, gap=0.0001, skip=60.0)[source]¶

Used to iterate over some given messages in the recorded time.

Creates an new MessageSync instance.

Parameters:

messages (Iterable[Message]) – An iterable of can.Message instances.
timestamps (bool) – Use the messages’ timestamps. If False, uses the gap parameter as the time between messages.
gap (float) – Minimum time between sent messages in seconds
skip (float) – Skip periods of inactivity greater than this (in seconds).

Example:

import can

with can.LogReader("my_logfile.asc") as reader, can.Bus(interface="virtual") as bus:
    for msg in can.MessageSync(messages=reader):
        print(msg)
        bus.send(msg)