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In computer programming, several language mechanisms exist for exception handling. The term exception is typically used to denote a data structure storing information about an exceptional condition. One mechanism to transfer control, or raise an exception, is known as a throw; the exception is said to be thrown. Execution is transferred to a catch.
C does not provide direct support to exception handling: it is the programmer's responsibility to prevent errors in the first place and test return values from the functions.
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.
The raise statement, used to raise a specified exception or re-raise a caught exception; The class statement, which executes a block of code and attaches its local namespace to a class, for use in object-oriented programming; The def statement, which defines a function or method
Raise exception: Try instructions Catch «exception» instructions... «Finally instructions» End Try — Python: raise exception: try: Tab ↹instructions except «exception»: Tab ↹instructions... «else: Tab ↹instructions» «finally: Tab ↹instructions» assert condition: Fortran — Forth: code THROW: xt CATCH ( code or 0 ) — OCaml ...
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. The original stacktrace is lost, along with the type of the original exception, any exception for which the original exception was a wrapper, and any other information captured in the ...
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 method returns to the code that invoked it when it completes all the statements in the method, reaches a return statement, or throws an exception, whichever occurs first. You declare a method's return type in its method declaration. Within the body of the method, you use the return statement to return the value.