'Ball' object has no attribute 'append'

This error message typically occurs when you try to use the `append()` method on an object that does not support it. In this case, it seems that you are trying to append to an object called `Ball`, which does not have an `append()` method.

Without more context or code, it's difficult to provide a more specific solution. However, some common reasons why you might see this error message include:

- You are trying to use the `append()` method on a non-list object. For example, if you create a `Ball` object using a class definition that does not define an `append()` method, you will not be able to use `append()` on that object.
- You are misspelling the name of the method or variable that you are trying to use. Double-check that you are using the correct syntax and spelling for the object you are trying to append to.
- You are trying to append to a variable that has not been initialized or defined yet. Make sure that you have created the object and assigned it a value before trying to append to it.

Again, without more information about your code and what you are trying to accomplish, it's difficult to provide a more specific solution.