Re: [Numpy-discussion] Handling named temporary files in tests

March 9, 2009

      A Monday 09 March 2009, David Cournapeau escrigué:
...
Hi,
While fixing several windows specific unit test failures, I
encountered some problems I am not sure how to solve. In particular,
we have a relatively common idiom as follows:
Open file securely with a visible name (using NamedTemporaryFile)
write some content into it
open the file with another open call
Of course, this does not work on windows. NamedTemporaryFile is
basically useless on this platform (windows refuses to let a process
to reopen a file opened from NamedTemporaryFile). I can see two
solutions: - using mkstemp + re-opening the file later from the name
returned by mkstemp: AFAICT, this basically defeats the whole purpose
of mkstemp - have our own layer to bypass mkstemp on windows, where
security is not a concern anyway, and use the proper functions on
sane platforms.
Do people have an opinion on this ? Or maybe a solution to the
problem altogether ?
We have a similar case of use for the PyTables project, and we ended 
implementing a class that is meant to be used as a mixin from which the 
test classes inherits.  The class is, more or less:

class TempFileMixin:
    def setUp(self):
        """Set ``h5file`` and ``h5fname`` instance attributes."""
        self.h5fname = tempfile.mktemp(suffix='.h5')
        self.h5file = tables.openFile(
            self.h5fname, 'w', title=self._getName())

    def tearDown(self):
        """Close ``h5file`` and remove ``h5fname``."""
        self.h5file.close()
        self.h5file = None
        os.remove(self.h5fname)

    def _reopen(self, mode='r'):
        """Reopen ``h5file`` in the specified ``mode``."""
        self.h5file.close()
        self.h5file = tables.openFile(self.h5fname, mode)
        return True

The advantage is that, by simply inheriting from `TempFileMixin`, the 
developer have avaliable the ``h5file`` (file handler) and ``h5fname`` 
(file name).  The mixin is responsible to open, close and remove the 
temporary file.  In addition, the `_reopen()` method allows you to 
manually close and re-open the temporary, if that is what you want.

An example of use:

# Test for building very large MD columns without defaults
class MDLargeColTestCase(common.TempFileMixin, common.PyTablesTestCase):
    reopen = True

    def test01_create(self):
        "Create a Table with a very large MD column.  Ticket #211."
        N = 2**18
        cols = {'col1': Int8Col(shape=N, dflt=0)}
        tbl = self.h5file.createTable('/', 'test', cols)
        tbl.row.append()   # add a single row
        tbl.flush()
        if self.reopen:
            self._reopen()
            tbl = self.h5file.root.test
        # Check the value
        assert allequal(tbl[0]['col1'], zeros(N, 'i1'))

This proved to be pretty handy in practice.

HTH,

-- 
Francesc Alted