ABSTRACT
People will misunderstand how to use programs, so software authors should plan from the start to detect and handle errors. Something that goes wrong while a program is running is referred to as an exception from normal behavior. When an exception is raised it can be caught and handled via blocks. Python organizes its standard exceptions in a hierarchy so that programs can catch and handle them selectively. Generally speaking, there is distinction between two types of errors/exceptions. Internal errors are mistakes in the program itself, such as calling a function with instead of a list. External errors are usually caused by interactions between the program and the outside world: a user may mis-type a filename, the network might be down, and so on. Error messages should be written so that they are informative to users of the program, and point to what can be done to fix the issue at hands. To report on program activity such as errors a proper logging framework should be used rather than statements. This facilitates separating logging messages into various levels according to their severity.
