try/except. Our version of the
oops
function follows. As for the noncoding questions, changingoops
to raiseKeyError
instead ofIndexError
means 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 namesKeyError
andIndexError
come from the outermost built-in names scope. If you don’t believe us, importbuiltin
__ and pass it as an argument to thedir
function to see for yourself.%
cat oops.py
def 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.py
caught an index error!Exception lists. Here’s the way we extended this module for an exception of our own:
%
cat oops.py
MyError = '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.py
caught 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.
%
cat safe2.py
import 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.py
Traceback ...
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