Python 3 - Second Edition

20    Exception Handling

Imagine a program that has a comparatively deep call hierarchy; that is, functions call other subfunctions, which in turn call functions again. It’s often the case that the higher-level functions can’t continue working correctly if an error has occurred in one of their subfunctions. The information that an error has occurred must therefore be passed up through the call hierarchy so that each higher-level function can react to the error and adapt to it.

20.1    Exceptions

Up to this point, you’ve been able to identify errors that occurred within a function solely on the basis of the function's return value. It takes a lot of effort to pass such a return value up through the function hierarchy, especially because they are ...