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A different view of exceptions is based on the principles of design by contract and is supported in particular by the Eiffel language. The idea is to provide a more rigorous basis for exception handling by defining precisely what is "normal" and "abnormal" behavior. Specifically, the approach is based on two concepts:
Try {Import-Module ActiveDirectory} Catch [Exception1] {# Statements that execute in the event of an exception, matching the exception} Catch [Exception2],[Exception3etc] {# Statements that execute in the event of an exception, matching any of the exceptions} Catch {# Statements that execute in the event of an exception, not handled more ...
In general, an exception breaks the normal flow of execution and executes a pre-registered exception handler; the details of how this is done depend on whether it is a hardware or software exception and how the software exception is implemented. Exceptions are defined by different layers of a computer system, and the typical layers are CPU ...
The try statement, which allows exceptions raised in its attached code block to be caught and handled by except clauses (or new syntax except* in Python 3.11 for exception groups [97]); it also ensures that clean-up code in a finally block is always run regardless of how the block exits
Exception swallowing can also happen if the exception is handled and rethrown as a different exception, discarding the original exception and all its context. In this C# example, all exceptions are caught regardless of type, and a new generic exception is thrown, keeping only the message of the original exception.
In a language that supports formal exception handling, a graceful exit may be the final step in the handling of an exception. In other languages graceful exits can be implemented with additional statements at the locations of possible errors.
Python sets are very much like mathematical sets, and support operations like set intersection and union. Python also features a frozenset class for immutable sets, see Collection types. Dictionaries (class dict) are mutable mappings tying keys and corresponding values. Python has special syntax to create dictionaries ({key: value})
A number of languages implement a form of switch statement in exception handling, where if an exception is raised in a block, a separate branch is chosen, depending on the exception. In some cases a default branch, if no exception is raised, is also present. An early example is Modula-3, which use the TRY...