'NoneType' object has no attribute 'append'

This error occurs when you try to use the append method on a variable that is of type None instead of a list.

For example, if you have a variable called my_list that is supposed to be a list, but it is assigned None instead:

my_list = None

And then you try to append an item to it:

my_list.append("item")

You will get the error 'NoneType' object has no attribute 'append'.

To fix this error, make sure that the variable is actually a list before using the append method on it. You can do this by initializing the variable as an empty list:

my_list = []

Or by making sure that the variable is assigned a list object before using the append method on it.