try/except. Our version of the
oopsfunction follows. As for the noncoding questions, changingoopsto raiseKeyErrorinstead ofIndexErrormeans that the exception won’t be caught by our try handler (it “percolates” to the top level and triggers Python’s default error message). The namesKeyErrorandIndexErrorcome from the outermost built-in names scope. If you don’t believe us, import_ _builtin__ and pass it as an argument to thedirfunction to see for yourself.%
cat oops.pydef oops(): raise IndexError def doomed(): try: oops() except IndexError: print 'caught an index error!' else: print 'no error caught...' if __name__ == '__main__': doomed() %python oops.pycaught an index error!Exception lists. Here’s the way we extended this module for an exception of our own:
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cat oops.pyMyError = 'hello' def oops(): raise MyError, 'world' def doomed(): try: oops() except IndexError: print 'caught an index error!' except MyError, data: print 'caught error:', MyError, data else: print 'no error caught...' if __name__ == '__main__': doomed() %python oops.pycaught error: hello worldError handling. Finally, here’s one way to solve this one; we decided to do our tests in a file, rather than interactively, but the results are about the same.
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cat safe2.pyimport sys, traceback def safe(entry, *args): try: apply(entry, args) # catch everything else except: traceback.print_exc() print 'Got', sys.exc_type, sys.exc_value import oops safe(oops.oops) %python safe2.pyTraceback ...