Python Object-Oriented Programming - Fifth Edition

Chapter 4 Expecting the Unexpected

Software is rugged; computer systems, however, can be fragile. While the software is highly predictable, the runtime context can provide unexpected inputs and situations. Devices fail, networks are unreliable, and mere anarchy is let loose on our application. We need to have a way to handle the spectrum of failures that plague complicated systems such as modern computers.

There are two broad approaches to dealing with the unforeseen. One approach is to return a recognizable error-signaling value from a function. A value, such as None, could be used. Other library functions can then be used by an application to retrieve details of the erroneous condition. A variation on this theme is to pair the return value ...