Musings: Using decorators to reduce duplicate exception handling

J Kenneth King james at
Wed Feb 18 00:12:57 CET 2009

I recently started a project called TracShell
( where I make heavy use of the
xmlrpclib core module.

When the number of RPC calls was small, wrapping each call in try/except
was acceptable. However, this obviously will duplicate code all over the
place. There are only ever two exceptions that the module itself will
throw: xmlrpclib.ProtocolError and xmlrpclib.Fault -- both very useful,
but not show stoppers.

To combat the duplication, my clever idea was to use a function
decorator to wrap any function that used xmlrpclib calls:

def catch_errors(fn):
    A decorator to catch typical xmlrpclib exceptions
    def wrapped(*args, **kwargs):
            return fn(*args, **kwargs)
        except xmlrpclib.ProtocolError, e:
            print "There was a problem communicating with the server."
            print "URL: %s" % e.url
            print "Headers: %s" % e.headers
            print "Error code: %d" % e.errcode
            print "Error message: %s" % e.errmsg
            print "Please file a report with the TracShell developers."
        except xmlrpclib.Fault, e:
            print "A fault ocurred"
            print "Fault code: %d" % e.faultCode
            print "Fault string: %s" % e.faultString
            print "If you think this message is the result of an error,"
            print "please file a report with the TracShell developers."
    return wrapped

Maybe I could rename the decorator to something meaningful, but besides
that it works pretty well. Now any function I write in my class that
uses RPC calls can be wrapped by this decorator and have the exception
handling done in a uniform way for these particular exceptions.

I was just curious if other Pythonistas out there used the same idea or
have a better one. Thoughts?

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