[py-dev] intermittent bugs in pytest/python on osx lion ?

Ian Miers imichaelmiers at gmail.com
Sat Jun 16 02:32:50 CEST 2012

Hi, I just started using pytest. It's lovely.
The TLDR on this is we are getting intermittent non reproducible errors
 that change and sometimes disappear between test runs like the following :
>   import os.path
E   TypeError: __import__() argument 1 must be str without null bytes, not

Longer version:
We've been getting buggy results out of test runs on OSX Lion with python
3.2.3  and  py.test version 2.2.4. Specifically we've been getting what
appear to be false-positive  test failures that change from run to run  and
cannot be reproduced by running some code ourselves or in the case of
doctest manually running  python3.2 -m doctest file.

Some of these errors will stay around for multiple test runs even after
make clean, etc. Some will change from run to run. All of them
eventually disappeared  temporarily and we got a clean test pass, though
how I don't know. Morever, the problems cropped up again. All of this was
with no code changes and code known to work on ubuntu and partially
manually tested on OSX.

Ordinarly I'd say there was something wrong with our code. However, some of
the errors are vanishingly unlikely. Claims that modules don't exist when
they do and are importable via python3.2 -c "from foo.bar.baz import narf"
and such.

The most glaringly, however, is this gem:
charm/toolbox/pairinggroup.py:3: in <module>
>   import os.path
E   TypeError: __import__() argument 1 must be str without null bytes, not

We also got a lovely bug where it appeared __pycache__  was corrupted
during test runs.  On an initial run, we could import a function from a
python c extension. On subsequent runs, it didn't exist. The function was
still in the .so file, as shown by nm, however help(module) returned
function_name#$@^%#$% Function description. Deleting __pychache__ folders
 resolved it for the next test run but then it came back. It too
disappeared after a couple of test runs never to be seen since.

Has anyone seen anyhting like this? Are their known issues on OSX with
python ? With pytest? Does anyone have any idea how I might get a better
idea whats going on?

As an addendum, the latest error I am getting is now :
>   test = [hashFn(struct.pack(">%dsI" % (len(seed)), seed, i)) for i in
E   UnicodeEncodeError: 'ascii' codec can't encode character '\x9e' in
position 0: ordinal not in range(128
This actually might be in our code,though again it works on ubuntu and at
one point on OSX.  Given that its a pattern that points to python or pytest
doing something  to binaries,  I'm including it anyway.

The project is charm, you can see the code on this branch here via
https://github.com/JHUISI/charm/tree/dev. Python was installed via fenc ( I
think, its not my box). The errors happened both with python3.2 -m pytest
 and with python3.2 setup.py test.  Though it appears more so with the


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