Check that an exception is correctly raised in Python 2.7?

问题

Does anyone know how to check that an exception is raised correctly?

I need something that works in Python 2.7. The below 'assert' is not quite correct method to use from the Python unittest library:

assert ( a_a0_getinst.add_port("iTCK", ISC.PortType_INPUT) ), "Can't add duplicate port"

The error I get is:

Traceback (most recent call last):
  File "test_010_module.py", line 157, in runTest
    a_a0_addinst = a_a0.add_instance( "A00", b_a0 )
  File "/nfs/sc/disks/sc_dteg_2004/users/acheung1/dteg_tools-isc/python/t/ISC.py", line 475, in add_instance
    return _ISC.SharedModule_add_instance(self, name, module)
RuntimeError: Can't add duplicate instance with instance name 'A00' to module 'A_A0'

---

回答1:

If you just want to make sure it raises the correct type of exception, you can use:

self.assertRaises(RuntimeError, your_function, *args, **kwargs)

in a unittest.TestCase class. See the docs for assertRaises.

If you also want to check that it also has the correct error message, you can instead use:

self.assertRaisesRegexp(RuntimeError, "error message", your_function_call, *args, **kwargs)

in a unittest.TestCase class. Here are the docs for assertRaisesRegexp.

You can also do these as context managers, in which case you don't need to separate the arguments out:

with self.assertRaises(RuntimeError):
    your_function_call(arg1, arg2)

with self.assertRaisesRegexp(RuntimeError, "error message"):
    your_function_call(arg1, arg2)

Those are for Python 2.7, as you mentioned. For Python 3.x, assertRaises behaves the same, but the regular expression one is called assertRegex (no p).

EDIT: As pointed out in the comments, this only works if you're using unittest-style test classes. If you're using py.test, it has its own similar methods you can use.

来源：https://stackoverflow.com/questions/43814495/check-that-an-exception-is-correctly-raised-in-python-2-7