It is possible to write programs that handle selected exceptions. Look at the following example, which prints a table of inverses of some floating point numbers:
>>> numbers = [0.3333, 2.5, 0, 10] >>> for x in numbers: ... print x, ... try: ... print 1.0 / x ... except ZeroDivisionError: ... print '*** has no inverse ***' ... 0.3333 3.00030003 2.5 0.4 0 *** has no inverse *** 10 0.1 >>>The try statement works as follows.
... except (RuntimeError, TypeError, NameError): ... passThe last except clause may omit the exception name(s), to serve as a wildcard. Use this with extreme caution, since it is easy to mask a real programming error in this way!
When an exception occurs, it may have an associated value, also known as the exceptions's argument. The presence and type of the argument depend on the exception type. For exception types which have an argument, the except clause may specify a variable after the exception name (or list) to receive the argument's value, as follows:
>>> try: ... spam() ... except NameError, x: ... print 'name', x, 'undefined' ... name spam undefined >>>If an exception has an argument, it is printed as the last part (`detail') of the message for unhandled exceptions.
Exception handlers don't just handle exceptions if they occur immediately in the try clause, but also if they occur inside functions that are called (even indirectly) in the try clause. For example:
>>> def this_fails(): ... x = 1/0 ... >>> try: ... this_fails() ... except ZeroDivisionError, detail: ... print 'Handling run-time error:', detail ... Handling run-time error: integer division or modulo >>>