test error message in python 3

Question

I have the following test method

def test_fingerprintBadFormat(self):
    """
    A C{BadFingerPrintFormat} error is raised when unsupported
    formats are requested.
    """
    with self.assertRaises(keys.BadFingerPrintFormat) as em:
        keys.Key(self.rsaObj).fingerprint('sha256-base')
    self.assertEqual('Unsupported fingerprint format: sha256-base',
        em.exception.message)

Here is the exception class.

class BadFingerPrintFormat(Exception):
    """
    Raises when unsupported fingerprint formats are presented to fingerprint.
    """

this test method works perfectly fine in Python2 but fails in python 3 with the following message

builtins.AttributeError: 'BadFingerPrintFormat' object has no attribute 'message'

How can I test the error message in Python3. I don't like the idea of using asserRaisesRegex as it tests the regex rather than the exception message.

Can you shed some light on BadFingerPrintFormat?

Lajos Arpad
– Lajos Arpad

2016-08-16 13:04:29 +00:00
Commented Aug 16, 2016 at 13:04 — Lajos Arpad
– Lajos Arpad, Commented Aug 16, 2016 at 13:04
@LajosArpad I edited the question.

abhi
– abhi

2016-08-16 13:12:17 +00:00
Commented Aug 16, 2016 at 13:12 — abhi
– abhi, Commented Aug 16, 2016 at 13:12

Martijn Pieters · Accepted Answer · 2016-08-16 14:42:09Z

3

The .message attribute was removed from exceptions in Python 3. Use .args[0] instead:

self.assertEqual('Unsupported fingerprint format: sha256-base',
    em.exception.args[0])

or use str(em.exception) to get the same value:

self.assertEqual('Unsupported fingerprint format: sha256-base',
    str(em.exception))

This will work both on Python 2 and 3:

>>> class BadFingerPrintFormat(Exception):
...     """
...     Raises when unsupported fingerprint formats are presented to fingerprint.
...     """
...
>>> exception = BadFingerPrintFormat('Unsupported fingerprint format: sha256-base')
>>> exception.args
('Unsupported fingerprint format: sha256-base',)
>>> exception.args[0]
'Unsupported fingerprint format: sha256-base'
>>> str(exception)
'Unsupported fingerprint format: sha256-base'

answered Aug 16, 2016 at 14:42

Martijn Pieters

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