Chapter 6. Exceptions
Python
uses exceptions to communicate errors and anomalies. An
exception is an object that indicates an error
or anomalous condition. When Python detects an error, it raises an
exception; that is, it signals the occurrence of an anomalous
condition by passing an exception object to the exception-propagation
mechanism. Your code can also explicitly raise an exception by
executing a raise statement.
Handling an exception means receiving
the exception object from the propagation mechanism and performing
whatever actions are needed to deal with the anomalous situation. If
a program does not handle an exception, it terminates with an error
traceback message. However, a program can handle exceptions and keep
running despite errors or other abnormal conditions.
Python also uses exceptions to indicate some special situations that
are not errors, and are not even abnormal occurrences. For example,
as covered in Chapter 4, an
iterator's next method raises the
exception StopIteration when the iterator has no
more items. This is not an error, and it is not even an anomalous
condition, since most iterators run out of items eventually.
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