test_multi_cell_list fails in python 3.7

[Chris Dent]

Generators used in multi cell list handling raise StopIteration, which is not something python 3.7 likes. Efforts to add python 3.7 testing to nova [1] revealed this (and similar for neighboring tests):

nova.tests.unit.compute.test_multi_cell_list.TestBaseClass.test_with_failing_cells
----------------------------------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b' File "/mnt/share/cdentsrc/nova/nova/compute/multi_cell_list.py", line 101, in query_wrapper'
    b' for record in fn(ctx, *args, **kwargs):'
    b' File "/mnt/share/cdentsrc/nova/nova/compute/multi_cell_list.py", line 348, in do_query'
    b' **kwargs)'
    b' File "/mnt/share/cdentsrc/nova/nova/tests/unit/compute/test_multi_cell_list.py", line 356, in get_by_filters'
    b' raise exception.CellTimeout'
    b'nova.exception.CellTimeout: Timeout waiting for response from cell'
    b''
    b'During handling of the above exception, another exception occurred:'
    b''
    b'Traceback (most recent call last):'
    b' File "/mnt/share/cdentsrc/nova/nova/compute/multi_cell_list.py", line 108, in query_wrapper'
    b' raise StopIteration'
    b'StopIteration'
    b''
    b'The above exception was the direct cause of the following exception:'
    b''
    b'Traceback (most recent call last):'
    b' File "/mnt/share/cdentsrc/nova/.tox/py37/lib/python3.7/site-packages/mock/mock.py", line 1305, in patched'
    b' return func(*args, **keywargs)'
    b' File "/mnt/share/cdentsrc/nova/nova/tests/unit/compute/test_multi_cell_list.py", line 384, in test_with_failing_cells'
    b' self.assertEqual(50, len(list(result)))'
    b' File "/mnt/share/cdentsrc/nova/nova/compute/multi_cell_list.py", line 400, in get_records_sorted'
    b' item = next(feeder)'
    b' File "/mnt/share/cdentsrc/nova/.tox/py37/lib/python3.7/heapq.py", line 359, in merge'
    b' s[0] = next() # raises StopIteration when exhausted'
    b'RuntimeError: generator raised StopIteration'
    b''

According to pep 479 [2] the fix for this is to 'return' instead of 'raise StopIteration'.

[1] https://review.openstack.org/#/c/624055/
[2] https://www.python.org/dev/peps/pep-0479/#writing-backwards-and-forwards-compatible-code

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/624055
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=2ea552e019bd427b5b1709160a6ed7da9dd23fbd
Submitter: Zuul
Branch: master

commit 2ea552e019bd427b5b1709160a6ed7da9dd23fbd
Author: Chris Dent <email address hidden>
Date: Mon Dec 10 11:22:54 2018 +0000

    Add python 3.7 unit and functional tox jobs

    Without these, if you try to run tox -epy37,functional-py37 you'll
    get a successful tox run, but no actual tests are run, which is
    rather misleading. Given the generaly availability of python 3.7
    this is a bad thing.

    Running the tests under python 3.7 identified a few minor tests
    failures, also fixed here. Each is a result of a change in behavior in
    python 3.7:

    * printable unicode changes with a new Unicode 11-based unicodedata
      package
    * intentionally raising StopIteration in a generator is now considered a
      RuntimeError, 'return' should be used instead
    * an exception message is different beween python 3 and python 2, and the
      guard for it was mapping python 3.5 and 3.6 but not 3.7.

    zuul configuration is adjusted to add an experimental job for python 3.7
    unit. A functional test job is not added, because we don't have 3.6 yet,
    and we probably want to get through that first.

    Closes-Bug: #1807976
    Closes-Bug: #1807970
    Change-Id: I37779a12d3b36eb3dc7e2733d07fe0ed23ab3da6

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 19.0.0.0rc1 release candidate.