Bug : Motor and pin won't work

[Hrishi1999]

Hello,
I was just using Physics and I found a strange bug. Now, make a machine and erase everything. Make another machine again, stop, and then add a pin and a motor to an object. Then play, you will see that nor the motor would work nor the object would be stuck at the same place. Using physics 31

[quozl]

What does "make a machine" mean? I do see three of the four Show sample projects do not work and the fourth slows down and stops.

[Hrishi1999]

A machine (here) like for example use circle tool and add a motor.

[quozl]

Okay, thanks, I've reproduced the problem from your description; there's a lot more to it;

• stop the world, ctrl+space,
• select circle tool, ctrl+c,
• draw a circle,
• select motor tool, ctrl+m,
• place a motor in the centre of the circle,
• start the world, ctrl+space,
• observe spinning circle,
• erase all, ctrl+a,
• stop the world, ctrl+space,
• select circle tool, ctrl+c,
• draw a circle,
• select motor tool, ctrl+m,
• place a motor in the centre of the circle,
• start the world, ctrl+space,
• observe circle is not spinning and falls with gravity.

At this point, the erase all button is not sensitive.

Workaround is to restart Physics, however a Keep Error happens during Stop.

1484166694.100760 ERROR root: Error saving activity object to datastore
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/sugar3/activity/activity.py", line 1087, in _prepare_close
    self.save()
  File "/usr/lib/python2.7/dist-packages/sugar3/activity/activity.py", line 896, in save
    self.write_file(file_path)
  File "/usr/share/sugar/activities/Physics.activity/activity.py", line 127, in write_file
    self.game.write_file(file_path)
  File "/usr/share/sugar/activities/Physics.activity/physics.py", line 89, in write_file
    self.world.json_save(path, additional_data, serialize=True)
  File "/usr/share/sugar/activities/Physics.activity/myelements/elements.py", line 481, in json_save
    worldmodel = self.get_world_model(additional_vars, serialize)
  File "/usr/share/sugar/activities/Physics.activity/myelements/elements.py", line 547, in get_world_model
    modeljoint['body1'] = joint.bodyA.userData['saveid']
TypeError: 'NoneType' object has no attribute '__getitem__'

Another workaround is to use erase ctrl+e instead of erase all ctrl+a.

[Hrishi1999]

I am aware of the workaround but this gets annoying sometimes.
(sorry for reopening issue, my phone screen is a bit broken and it accidentally pressed close issue:()

[quozl]

No worries, I wasn't documenting the two workarounds for you only, but also for everybody else. It is common for the workaround(s) of a problem to go some way toward explaining the cause.

[quozl]

12c5f70 fixes the traceback mentioned above, but not the other problems.