Obscure error in getPathforOid

[ale-rt]

While debugging an issue with @pysailor we found that a try/except in getPathForOID is masking an OSError with an AssertionError:

ZODB/src/ZODB/blob.py

Lines 432 to 435 in 8f5ac63

	except OSError:
	# We might have lost a race. If so, the directory
	# must exist now
	assert os.path.exists(path)

At least logging the OSError would help understanding what is wrong (in our case it was related to the fact that we had no more inode available in the filesystem).

[ale-rt]

Any suggestion for a future PR?

Given that assertion are stripped when the -O flag is set is that code safe at all? See:

[ale@emily ~]$ cat tmp/a.py
assert False
print("Hello world!")
[ale@emily ~]$ python3 tmp/a.py
Traceback (most recent call last):
  File "tmp/a.py", line 1, in <module>
    assert False
AssertionError
[ale@emily ~]$ python3 -O tmp/a.py
Hello world!

Should not we just raise the OSError if the directory does not exist?

[tseaver]

Should not we just raise the OSError if the directory does not exist?

I'm not sure: the point of the try: ... except OSError: block is to ensure that the directory exists: if another thread / process has created it, then the function can return normally. I guess we could check the errno of the exception, e.g.:

        if create and not os.path.exists(path):
            try:
                os.makedirs(path)
            except OSError as exc:
                # We might have lost a race.  If so, the directory
                # must exist now
                if exc.errno != errno.EEXIST:
                    raise
                assert os.path.exists(path)
        return path