ROS2 Python: Add arguments to callback

asked 2020-03-16 08:05:40 -0600

ninamwa
81 ●10 ●13 ●15

Hi. I am using Python and ROS2 and I want to create two action clients: One for opening a gripper and one for closing it. The goal_response_callback is completely similar for both, and the result callback is very similar, it just changes what parameter to set to true/false. Instead of having two goal_callbacks and two result_callbacks, i was hoping to just give in an argument saying if the goal was to open or close the gripper, but i can't seem to find the correct way to use the callback together with an argument. I have tried to just give the argument as normal (self.goal_response_callback("open"), and as a partial function shown in the code below. Nothing seems to work.

Anyone who can tell me the best way to do this? Thanks!

 def send_close_gripper_goal(self):
    goal_msg = CloseGripper.Goal()
    self.closegripper_action_client.wait_for_server()
    self._send_goal_future = self.closegripper_action_client.send_goal_async(goal_msg)
    self._send_goal_future.add_done_callback(partial(self.goal_response_callback,"close"))

def goal_response_callback(self, future,type):
    goal_handle = future.result()
    if not goal_handle.accepted:
        self.get_logger().info('Goal rejected :(')
        return

    self.get_logger().info('Goal accepted :)')
    self._get_result_future = goal_handle.get_result_async()
    self._get_result_future.add_done_callback(self.get_result_callback(type))

def get_result_callback(self,future,type):
    result = future.result().result
    if type == "open":
        GripperOpen = result.success
        GripperClose = not result.success
    if type == "close":
        GripperClose = result.success
        GripperOpen = not result.success
    print(GripperClose)
    print(GripperOpen)

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answered 2020-03-16 11:58:19 -0600

sloretz
3061 ●25 ●86 ●55

I think the problem is functools.partial is providing the first argument instead of the second. Use keyword arguments to disambiguate.

>>> import functools
>>> def my_func(result, type):
...    print(f'Got {result} and {type}')
... 
>>> my_func('foo', 'bar')
Got foo and bar
>>> functools.partial(my_func, 'close')('foo')
Got close and foo
>>> functools.partial(my_func, type='close')('foo')
Got foo and close

More specifically, change the call to add_done_callback to:

self._send_goal_future.add_done_callback(partial(self.goal_response_callback, type="close"))

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Thank you, this worked exactly as I wanted! :-)

ninamwa ( 2020-03-17 04:43:16 -0600 )edit

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answered 2022-03-01 08:13:41 -0600

George V
11 ●2 ●2

If you don't want to import 'functools' you can also do it with lambda functions:

>>> def foobar(a,b):
...     return a+b
>>> foobar(1,2) # call normal function
3

>>> bind = lambda x: foobar(x, 2) # bind 2 to foobar
>>> bind(1) 
3

>>> bind = lambda: foobar(1,2) # bind all elements  
>>> bind()  
3

So in your case it would look like:

self._send_goal_future.add_done_callback( lambda future: self.goal_response_callback(future, "close"))

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