Improve import_from_dotted_path error message

[LilyFirefly]

• Avoid exposing rsplit implementation detail in exception message.
• Fix Improve error message on nav_tree.utils.import_from_dotted_path #28.

[coveralls]

Coverage remained the same when pulling 843e6d0 on Ian-Foote:error-message into 9a7e03b on meshy:master.

[meshy]

Oooh python 3 shiny! I've not used this feature yet... what is the advantage of using from None here?

[LilyFirefly]

It hides the fact that this exception was caused by rsplit raising ValueError - the end user doesn't need to know that implementation detail.

See Pep 409 for more detail.

[meshy]

I take it that it does still show the stacktrace, though?

[LilyFirefly]

>>> try:
...  1/0
... except ZeroDivisionError:
...  raise TypeError
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
TypeError

>>> try:
...  1/0
... except ZeroDivisionError:
...  raise TypeError from None
... 
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
TypeError

[meshy]

👍