Add function to get Exception.message

[dgingrich]

• Add exception_message
• Move reraise _add_doc to right after definition

Manual py.test runs with Python2.6 and 3.5 passed, but tox failed with AttributeError: 'module' object has no attribute 'exception_message'.

[benjaminp]

Thanks for the PR. What prevents you from using str(some_exception) in both Python 2 and 3?

[dgingrich]

Unicode strings get decode errors in Python 2:

>>> e = Exception(u'unicöde')
>>> e.message
u'unic\xf6de'
>>> str(e)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xf6' in position 4: ordinal not in range(128)

There is a workaround using six.text_type:

# Python2.6
>>> import six
>>> six.text_type(Exception(u"unicöde"))
u'unic\xf6de'

In addition this shouldn't be much of a problem since Exception.message has been deprecated since 2.6, so I understand if you the PR is rejected. The missing .message attribute does come up in the real world though, this was prompted by another PR for Spark: apache/spark#16845

[benjaminp]

Yeah, I was going to suggest your six.text_type approach or e.args[0] to deal with unicode.

You're right that I don't want to support deprecated features if possible. Thanks for the suggestion, though.