Built-in exceptions are all named with a leading upper-case
letter. This makes them consistent with class names, which also begin
with a leading upper-case letter.
Most modules or classes will have a single built-in exception,
Error. This exception will
be imported from a module, and can then be qualified by the module name.
Modules and module qualification is covered in Part IV, “Components, Modules and Packages”. It is not typical to have a complex hierarchy of
exceptional conditions defined by a module.