I got this error:
AttributeError: 'NoneType' object has no attribute 'something'
What general scenarios might cause such an AttributeError, and how can I identify the problem?
This is a special case of AttributeErrors. It merits separate treatment because there are a lot of ways to get an unexpected None value from the code, so it's typically a different problem; for other AttributeErrors, the problem might just as easily be the attribute name.
See also What is a None value? and What is a 'NoneType' object? for an understanding of None and its type, NoneType.