On Fri, 24 Oct 2008 01:47:10 -0700, Rafe wrote:
> Hi,
>
> I've encountered a problem which is making debugging less obvious than
> it should be. The @property decorator doesn't always raise exceptions.
I don't think that's the problem. I think properties do correctly raise
all exceptions that occur inside them, at least built-in exceptions.
I wrote a test that raises exceptions inside properties and they (almost)
all are raised normally.
Whatever your problem is, it isn't that properties don't raise exceptions.
For those who are interested, the test program I used follows.
# test module
def get_exceptions():
import __builtin__
list_of_exceptions = []
for key in dir(__builtin__):
# do not use __builtins__ -- note the 's'.
obj = getattr(__builtin__, key)
if not isinstance(obj, type):
continue
if issubclass(obj, Exception):
list_of_exceptions.append(obj)
return list_of_exceptions
def builder(list_of_exceptions):
class PropertyTester(object):
"""Do properties raise exceptions? Let's find out."""
for exception in list_of_exceptions:
name = exception.__name__
@property
def func(self, exception=exception):
# Make sure we bind a local copy to exception.
raise exception
setattr(PropertyTester, name, func)
return PropertyTester()
def testRaises(obj, exception_type, verbose):
"""Test that appropriate exception is raised when accessing an
attribute."""
name = exception_type.__name__
try:
getattr(obj, name)
except exception_type:
if verbose:
print "Passed: expected exception %s raised correctly" \
% exception_type
except Exception, e:
print "Failed: expected %s but got %r" % (exception_type, e)
else:
print "Failed: expected %s but got no exception at all" \
% exception_type
if __name__ == '__main__':
import sys
if sys.argv[1:] == ['verbose']:
verbose = True
else:
verbose = False
exceptions = get_exceptions()
tester = builder(exceptions)
for exception in exceptions:
testRaises(tester, exception, verbose)
--
Steven
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