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try {// Normal execution path. throw new EmptyStackException ();} catch (ExampleException ee) {// Deal with the ExampleException.} finally {// Always run when leaving the try block (including finally clauses), regardless of whether any exceptions were thrown or whether they were handled. // Often used to clean up and close resources such a file ...
An example of a programming language construct which may or may not terminate is a loop, as they can be run repeatedly. Loops implemented using a counter variable as typically found in data processing algorithms will usually terminate, demonstrated by the pseudocode example below:
Exceptions can be used to represent and handle abnormal, unpredictable, erroneous situations, but also as flow control structures to handle normal situations. For example, Python's iterators throw StopIteration exceptions to signal that there are no further items produced by the iterator. [1]
The else clause in the above example is linked to the for statement, and not the inner if statement. Both Python's for and while loops support such an else clause, which is executed only if early exit of the loop has not occurred. Some languages support breaking out of nested loops; in theory circles, these are called multi-level breaks.
A notable example of this is Python, where = is not an operator, but rather just a separator in the assignment statement. Although Python allows multiple assignments as each assignment were an expression, this is simply a special case of the assignment statement built into the language grammar rather than a true expression. [10]
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: raise exception: try expression with pattern-> expression ... assert condition: F#: try expression with ...
A conditional loop has the potential to become an infinite loop when nothing in the loop's body can affect the outcome of the loop's conditional statement. However, infinite loops can sometimes be used purposely, often with an exit from the loop built into the loop implementation for every computer language , but many share the same basic ...
However, a generator is an object with persistent state, which can repeatedly enter and leave the same scope. A generator call can then be used in place of a list, or other structure whose elements will be iterated over. Whenever the for loop in the example requires the next item, the generator is called, and yields the next item.