Check compatibility with python-can 4.0.0

[acolomb]

We should make sure there are no incompatible API changes regarding python-canopen's usage of the python-can package version 4.0.0 released today.

If there are, I suggest to release a version 3.0.1 here which pins the requirement to the last python-can release 3.3.x.

Then when any incompatibilities are addressed, make a version 3.1.0 that depends on python-can >=4.0.0 of required or just keep >=3.0.0 and remove the limitation <4.0.0 again.

If we are already compatible after thorough testing, this issue can just be closed.

[christiansandberg]

I'm not aware of any changes that affects us directly, but I haven't tested anything. Hopefully the tests will catch any incompatibilities since some tests check the integration with python-can.

[VonSquiggles]

I am seeing incompatibility with python-can version 4.0.0 using an ixxat device. between versions 3 and 4 they expanded their API to support different models of the ixxat tool (CAN FD vs non-FD), and their IXXATBus class now has a 'bus' attribute that is specific to the device model. Thus, my network object now has self.bus AND self.bus.bus, not just self.bus.

"""
Traceback (most recent call last):
File "C:...\CreatingAMenu.py", line 182, in
SendSyncMessage(0.1, 6)
File "C:...\CreatingAMenu.py", line 125, in SendSyncMessage
NETWORK.sync.start(sendInterval)
File "C:\Program Files\Python310\lib\site-packages\canopen\sync.py", line 38, in start
self._task = self.network.send_periodic(self.cob_id, [], self.period)
File "C:\Program Files\Python310\lib\site-packages\canopen\network.py", line 233, in send_periodic
return PeriodicMessageTask(can_id, data, period, self.bus, remote)
File "C:\Program Files\Python310\lib\site-packages\canopen\network.py", line 315, in init
self._start()
File "C:\Program Files\Python310\lib\site-packages\canopen\network.py", line 318, in _start
self._task = self.bus.send_periodic(self.msg, self.period)
File "C:\Program Files\Python310\lib\site-packages\can\bus.py", line 239, in send_periodic
periodic_tasks = self._periodic_tasks
AttributeError: 'IXXATBus' object has no attribute '_periodic_tasks'
"""

^ If I change line 233 in canopen\network.py to be "PeriodicMessageTask(can_id, data, period, self.bus.bus, remote)", I no longer get an error, but my sync message sends at seemingly the fastest rate possible. I am less familiar with threads so will likely not be able to tackle this myself.

[christiansandberg]

This is a bug in python-can. The IXXAT interface does not call the base class init method.

[VonSquiggles]

@christiansandberg The interface calls another class depending on the driver, which then calls the base class init method. It's not a bug - just an API change.

[christiansandberg]

If you try to use the send_periodic method outside of CANopen you will probably find that it doesn't work there either. The bus inside a bus is implementation specific to IXXAT and should be transparent to the API consumer.

[VonSquiggles]

You're right. Looks like hardbyte/python-can#1285 calls out that specific issue.

It should be made known to user that v4.0.0 is incompatible, even if it is due to known bugs on python-can side.

[VonSquiggles]

Opened pull request to remove python-can >=v4.0.0 as dependency option

[christiansandberg]

It's complicated since the bug is limited to a specific interface. Most users will not be affected and forcing a downgrade for everyone else may cause bigger issues. We still allow python-can 3.x so IXXAT users could still downgrade python-can until the issue is fixed. Maybe add a note to the README?

[fs570714]

I already answered here #318 just for those who are looking for a solution to their problem with the IXXAT, this issue is solved with the pull request hardbyte/python-can#1532 of the python-can library.