Why isn't the exception caught by << try >>?

I have a Python (Django) unit test FAIL from an exception, but the failing code is in a try / except block written for that exception. A similar block handles the exception when it is directly raised.

This passes:

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#   Code catches a directly raised ImmediateHttpResponse
try:
    raise ImmediateHttpResponse(response=auth_result)
    self.fail()
except ImmediateHttpResponse, e:
    self.assertTrue(True)

This, immediately following it, fails:

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#   FAIL
try:
    resp = resource.dispatch_list(request)  #<--- Line 172
    self.fail()
except ImmediateHttpResponse, e:
    self.assertTrue(True)

Here is the trace:

Traceback (most recent call last):
  File ".../web_app/tests/api/tastypie_authentication.py", line 172, in test_dispatch_list_d开发者_C百科iagnostic
  resource.dispatch_list(request)
  File ".../libraries/django_tastypie/tastypie/resources.py", line 410, in dispatch_list
  return self.dispatch('list', request, **kwargs)
  File ".../libraries/django_tastypie/tastypie/resources.py", line 434, in dispatch
  self.is_authenticated(request)
  File ".../libraries/django_tastypie/tastypie/resources.py", line 534, in is_authenticated
  raise ImmediateHttpResponse(response=auth_result)
ImmediateHttpResponse

Per the trace, the dispatch_list() call fails because it raises an << ImmediateHttpResponse >> exception. But placing just such an exception in the try block does not create a similar failure.

Why is the try / except block handling the one exception but not the other?

Note that the test code is copied from a library's test code, which does run as expected. (I'm using the library test code to diagnose my own implementation failures.)

---

Did you define your own ImmediateHttpResponse? (I so, do not do that.) It's possible to get the symptom you are describing if tastypie is raising a tastypie.exceptions.ImmediateHttpResponse while your unit test is testing for a locally defined ImmediateHttpResponse.

If so, to fix the problem, delete your definition of ImmediateHttpResponse and put something like

from tastypie.exceptions import ImmediateHttpResponse

in your unit test instead.

---

Got it, the problem was that my import of ImmediateHttpException differed from that of the code raising the error.

My import statement was:

from convoluted.directory.structure.tastypie.exceptions import ImmediateHttpResponse

The resource.py code that threw the error used:

from tastypie.exceptions import ImmediateHttpResponse

So it raised an exception != to the one I imported, though their string outputs were the same.

Fixing my import statement resolved the problem.

Thanks for listening!