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The implementation of exception handling in programming languages typically involves a fair amount of support from both a code generator and the runtime system accompanying a compiler. (It was the addition of exception handling to C++ that ended the useful lifetime of the original C++ compiler, Cfront. [18]) Two schemes are most common.
The Perl mechanism for exception handling uses die to throw an exception when wrapped inside an eval {...}; block. After the eval, the special variable $@ contains the value passed from die. Perl 5.005 added the ability to throw objects as well as strings. This allows better introspection and handling of types of exceptions.
An exception handling mechanism allows the procedure to raise an exception [2] if this precondition is violated, [1] for example if the procedure has been called on an abnormal set of arguments. The exception handling mechanism then handles the exception. [3] The precondition, and the definition of exception, is subjective.
Python is a high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation. [33] Python is dynamically type-checked and garbage-collected. It supports multiple programming paradigms, including structured (particularly procedural), object-oriented and functional ...
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...
Exception chaining, or exception wrapping, is an object-oriented programming technique of handling exceptions by re-throwing a caught exception after wrapping it inside a new exception. The original exception is saved as a property (such as cause) of the new exception. The idea is that a method should throw exceptions defined at the same ...
Python's with statement and Ruby's block argument to File.open are used to similar effect. All the languages mentioned above define standard exceptions and the circumstances under which they are thrown.
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})