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Hello, I'm trying to run an object on Python with ROS. When I run the code with a variable inside the object:

class lk(old_image):
....then some code
  def main(args):
        rospy.init_node('lk', anonymous=True)
        old_image = lk(old_image)

        try:
            rospy.spin()
        except KeyboardInterrupt:
            print "Shutting down"
            #cv.DestroyAllWindows()
Traceback (most recent call last):
  File "/home/aadejare/ros/omnisensor/nodes/lk.py", line 12, in <module>
    class lk(old_image):

However when I get rid of the variable inside the class I then get:

Traceback (most recent call last):
  File "***", line 67, in <module>
    main(sys.argv)
NameError: name 'main' is not defined

What would be the cause of the NameError? I tried putting in the old_image variable as a global but the same thing occurs except it identifies the variable as global. Thanks for the help

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Last Post by griswolf
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What is purpose of replacing the parent class with instance of child class at line 5? I do not understand how it would function.

Your first error message looks incomplete.

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What is purpose of replacing the parent class with instance of child class at line 5? I do not understand how it would function.

Your first error message looks incomplete.

Sorry for that here's the error message

Traceback (most recent call last):
  File "/home/aadejare/ros/omnisensor/nodes/lk.py", line 12, in <module>
    class lk(old_image):
NameError: name 'old_image' is not defined

We want to modify the data so that whenever the function is called, the old image would be the previous image before it for instance, image 0 would replace image 1 at the end and ect.

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This: class lk(old_image):... declares a subclass of class old_image. I'm guessing that what you want is actually to initialize an instance of lk with the old image. You do that in lk's member function def __init__(self, old_image):... Of course this is only a guess at what you intended.

By the way, why is the main function a member of class lk?

Edited by griswolf: n/a

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This: class lk(old_image):... declares a subclass of class old_image. I'm guessing that what you want is actually to initialize an instance of lk with the old image. You do that in lk's member function def __init__(self, old_image):... Of course this is only a guess at what you intended.

By the way, why is the main function a member of class lk?

I want to use old_image as a variable that I can use throughout the code.
As for the main function, I am not so sure myself. I'm going to correct that.

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I want to use old_image as a variable that I can use throughout the code

Then you have done the wrong thing with your class declaration. You want something like

class Lk:
  def __init__(self, old_image):
     self.old_image = old_image # whatever you really want
  # other class methods

Then you would create an instance of Lk with lk_instance = Lk(old_image)

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Then you have done the wrong thing with your class declaration. You want something like

class Lk:
  def __init__(self, old_image):
     self.old_image = old_image # whatever you really want
  # other class methods

Then you would create an instance of Lk with lk_instance = Lk(old_image)

Okay, thank you but now I get this error

Traceback (most recent call last):
  File "***", line 68, in <module>
    main(sys.argv)
  File "***", line 59, in main
    old_image = lk(old_image)
UnboundLocalError: local variable 'old_image' referenced before assignment
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Looks like you are really lacking the fundamentals of Python.

I'm new to Python. I kind of jumped into the deep end and am now working my way through.

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