'NoneType' object is not subscriptable

This error occurs when you try to access an index or a key of a variable that has a value of None. In Python, None is a special value that represents the absence of a value. Therefore, you cannot perform any operations on it that require a value, like indexing or subscripting.

For example, consider the following code:

my_list = None
print(my_list[0])

This code will raise a TypeError with the message "'NoneType' object is not subscriptable" because my_list is None and you are trying to access the first element of a list that does not exist.

To avoid this error, you should check if the variable is None before trying to access its values. For example:

my_list = None
if my_list is not None:
    print(my_list[0])
else:
    print("my_list is None")

This code will print "my_list is None" because my_list is None and you cannot access its values.