Internal API

Here we document the odds and ends that are more helpful for creating your own interfaces or listeners but generally shouldn’t be required to interact with python-can.

Extending the BusABC class

Concrete implementations must implement the following:

  • send() to send individual messages

  • _recv_internal() to receive individual messages (see note below!)

  • set the channel_info attribute to a string describing the underlying bus and/or channel

They might implement the following:

  • flush_tx_buffer() to allow discarding any messages yet to be sent

  • shutdown() to override how the bus should shut down

  • _send_periodic_internal() to override the software based periodic sending and push it down to the kernel or hardware.

  • _apply_filters() to apply efficient filters to lower level systems like the OS kernel or hardware.

  • _detect_available_configs() to allow the interface to report which configurations are currently available for new connections.

  • state() property to allow reading and/or changing the bus state.

Note

TL;DR: Only override _recv_internal(), never recv() directly.

Previously, concrete bus classes had to override recv() directly instead of _recv_internal(), but that has changed to allow the abstract base class to handle in-software message filtering as a fallback. All internal interfaces now implement that new behaviour. Older (custom) interfaces might still be implemented like that and thus might not provide message filtering:

Concrete instances are usually created by can.Bus which takes the users configuration into account.

Bus Internals

Several methods are not documented in the main can.BusABC as they are primarily useful for library developers as opposed to library users. This is the entire ABC bus class with all internal methods:

class can.BusABC(channel, can_filters=None, **kwargs)[source]

The CAN Bus Abstract Base Class that serves as the basis for all concrete interfaces.

This class may be used as an iterator over the received messages and as a context manager for auto-closing the bus when done using it.

Please refer to Errors for possible exceptions that may be thrown by certain operations on this bus.

Construct and open a CAN bus instance of the specified type.

Subclasses should call though this method with all given parameters as it handles generic tasks like applying filters.

Parameters

  • channel (Any) – The can interface identifier. Expected type is backend dependent.

  • can_filters (Optional[Sequence[Union[CanFilter, CanFilterExtended]]]) – See set_filters() for details.

  • kwargs (dict) – Any backend dependent configurations are passed in this dictionary

Raises

  • ValueError – If parameters are out of range

  • can.CanInterfaceNotImplementedError – If the driver cannot be accessed

  • can.CanInitializationError – If the bus cannot be initialized

About the IO module

Handling of the different file formats is implemented in can.io. Each file/IO type is within a separate module and ideally implements both a Reader and a Writer. The reader usually extends can.io.generic.BaseIOHandler, while the writer often additionally extends can.Listener, to be able to be passed directly to a can.Notifier.

Adding support for new file formats

This assumes that you want to add a new file format, called canstore. Ideally add both reading and writing support for the new file format, although this is not strictly required.

  1. Create a new module: can/io/canstore.py (or simply copy some existing one like can/io/csv.py)

  2. Implement a reader CanstoreReader (which often extends can.io.generic.BaseIOHandler, but does not have to). Besides from a constructor, only __iter__(self) needs to be implemented.

  3. Implement a writer CanstoreWriter (which often extends can.io.generic.BaseIOHandler and can.Listener, but does not have to). Besides from a constructor, only on_message_received(self, msg) needs to be implemented.

  4. Add a case to can.io.player.LogReader’s __new__().

  5. Document the two new classes (and possibly additional helpers) with docstrings and comments. Please mention features and limitations of the implementation.

  6. Add a short section to the bottom of doc/listeners.rst.

  7. Add tests where appropriate, for example by simply adding a test case called class TestCanstoreFileFormat(ReaderWriterTest) to test/logformats_test.py. That should already handle all of the general testing. Just follow the way the other tests in there do it.

  8. Add imports to can/__init__py and can/io/__init__py so that the new classes can be simply imported as from can import CanstoreReader, CanstoreWriter.

IO Utilities

Contains generic base classes for file IO.

class can.io.generic.BaseIOHandler(file, mode='rt')[source]

A generic file handler that can be used for reading and writing.

Can be used as a context manager.

Attr file

the file-like object that is kept internally, or None if none was opened

Parameters

  • file (Union[TextIO, BinaryIO, GzipFile, str, os.PathLike[str], None]) – 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 (str) – the mode that should be used to open the file, see open(), ignored if file is None

stop()[source]

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

Return type

None

class can.io.generic.FileIOMessageWriter(file, mode='rt')[source]

A specialized base class for all writers with file descriptors.

Parameters

  • file (Union[TextIO, BinaryIO, GzipFile, str, os.PathLike[str]]) – 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 (str) – the mode that should be used to open the file, see open(), ignored if file is None

class can.io.generic.MessageReader(file, mode='rt')[source]

The base class for all readers.

Parameters

  • file (Union[TextIO, BinaryIO, GzipFile, str, os.PathLike[str], None]) – 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 (str) – the mode that should be used to open the file, see open(), ignored if file is None

class can.io.generic.MessageWriter(file, mode='rt')[source]

The base class for all writers.

Parameters

  • file (Union[TextIO, BinaryIO, GzipFile, str, os.PathLike[str], None]) – 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 (str) – the mode that should be used to open the file, see open(), ignored if file is None

Other Utilities

Utilities and configuration file parsing.

can.util.channel2int(channel)[source]

Try to convert the channel to an integer.

Parameters

channel (Union[int, str, None]) – Channel string (e.g. “can0”, “CAN1”) or an integer

Return type

Optional[int]

Returns

Channel integer or None if unsuccessful

can.util.deprecated_args_alias(**aliases)[source]

Allows to rename/deprecate a function kwarg(s) and optionally have the deprecated kwarg(s) set as alias(es)

Example:

@deprecated_args_alias(oldArg=”new_arg”, anotherOldArg=”another_new_arg”) def library_function(new_arg, another_new_arg):

pass

@deprecated_args_alias(oldArg=”new_arg”, obsoleteOldArg=None) def library_function(new_arg):

pass

can.util.dlc2len(dlc)[source]

Calculate the data length from DLC.

Parameters

dlc (int) – DLC (0-15)

Return type

int

Returns

Data length in number of bytes (0-64)

can.util.len2dlc(length)[source]

Calculate the DLC from data length.

Parameters

length (int) – Length in number of bytes (0-64)

Return type

int

Returns

DLC (0-15)

can.util.load_config(path=None, config=None, context=None)[source]

Returns a dict with configuration details which is loaded from (in this order):

  • config

  • can.rc

  • Environment variables CAN_INTERFACE, CAN_CHANNEL, CAN_BITRATE

  • Config files /etc/can.conf or ~/.can or ~/.canrc where the latter may add or replace values of the former.

Interface can be any of the strings from can.VALID_INTERFACES for example: kvaser, socketcan, pcan, usb2can, ixxat, nican, virtual.

Note

The key bustype is copied to interface if that one is missing and does never appear in the result.

Parameters

  • path – Optional path to config file.

  • config – A dict which may set the ‘interface’, and/or the ‘channel’, or neither. It may set other values that are passed through.

  • context – Extra ‘context’ pass to config sources. This can be use to section other than ‘default’ in the configuration file.

Returns

A config dictionary that should contain ‘interface’ & ‘channel’:

{
    'interface': 'python-can backend interface to use',
    'channel': 'default channel to use',
    # possibly more
}

Note None will be used if all the options are exhausted without finding a value.

All unused values are passed from config over to this.

Raises

CanInterfaceNotImplementedError if the interface name isn’t recognized

can.util.load_environment_config(context=None)[source]

Loads config dict from environmental variables (if set):

  • CAN_INTERFACE

  • CAN_CHANNEL

  • CAN_BITRATE

  • CAN_CONFIG

if context is supplied, “_{context}” is appended to the environment variable name we will look at. For example if context=”ABC”:

  • CAN_INTERFACE_ABC

  • CAN_CHANNEL_ABC

  • CAN_BITRATE_ABC

  • CAN_CONFIG_ABC

Return type

Dict[str, str]

can.util.load_file_config(path=None, section='default')[source]

Loads configuration from file with following content:

[default]
interface = socketcan
channel = can0
Parameters

  • path – path to config file. If not specified, several sensible default locations are tried depending on platform.

  • section – name of the section to read configuration from.

can.util.set_logging_level(level_name)[source]

Set the logging level for the “can” logger.

Parameters

level_name (str) – One of: ‘critical’, ‘error’, ‘warning’, ‘info’,

‘debug’, ‘subdebug’, or the value None (=default). Defaults to ‘debug’.

Return type

None

can.util.time_perfcounter_correlation()[source]

Get the perf_counter value nearest to when time.time() is updated

Computed if the default timer used by time.time on this platform has a resolution higher than 10μs, otherwise the current time and perf_counter is directly returned. This was chosen as typical timer resolution on Linux/macOS is ~1μs, and the Windows platform can vary from ~500μs to 10ms.

Note this value is based on when time.time() is observed to update from Python, it is not directly returned by the operating system.

Return type

Tuple[float, float]

Returns

(t, performance_counter) time.time value and time.perf_counter value when the time.time is updated