Pyfakefs doesn't work with Python 2.6+ backport of os.scandir

[OskarPersson]

pyfakefs doesn't work with the backport of os.scandir Is this possible or does it have the same limitations as lxml?

Currently the backport, just like in #119, doesn't find any directories created by pyfakefs and raises an OSError:

OSError: [Errno 2] No such file or directory: 'root'

[mrbean-bremen]

Yes, unfortunately it has the same limitations as lxml. The backport is a C based module, and thus cannot be faked without explicit support in the library. Currently, we have no support for any non-standard libraries, and I'm not sure if that would be in the scope of this package. @jmcgeheeiv - what do you think?

[jmcgeheeiv]

If it's C/C++, it is technically infeasable to patch it and fake it.

…

On Thu, Dec 7, 2017 at 8:10 AM, mrbean-bremen ***@***.***> wrote: Yes, unfortunately it has the same limitations as lxml. The backport is a C based module, and thus cannot be faked without explicit support in the library. Currently, we have no support for any non-standard libraries, and I'm not sure if that would be in the scope of this package. @jmcgeheeiv <https://github.com/jmcgeheeiv> - what do you think? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#332 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADjLAREYeVjd_Jc5i2um0Ad7Rr3OHsRbks5s-A4GgaJpZM4Q5sq3> .

[mrbean-bremen]

Well, we could fake it the same way we fake os, I'm just not sure if this is the way to go. We already have a fake implementation of os.scandir, so that could be used in this case, e.g. we would have to fake out the scandir module in case it is available.

[mrbean-bremen]

I have thought about this a little more, and I think that we can refactor Patcher a little to be able to add other faked modules without the need to directly reference them in the patcher itself.
I may have a go at this after the pep8 stuff is merged.

[mrbean-bremen]

@OskarPersson - please check if this works for you and reopen otherwise.
Just learned that mentioning the issue in the PR description (not in the commit message) also auto-closes it...

[OskarPersson]

Hmm, no I can't get it to work :/

I cloned the master branch, created a new Python 2.7.14 virtualenv, pip installed scandir and tested with python all_tests.py. This resulted in 8 errors, all with the same traceback:

ERROR: testIndexAccessToStatTimesReturnsInt (fake_filesystem_test.FakeScandirTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/oskar/git/pyfakefs/fake_filesystem_test.py", line 4832, in setUp
    from fake_scandir import scandir
ImportError: No module named fake_scandir

---

I also tried setting up a simple test in example_test.py:

from scandir import scandir

def test_scandir_backport(self):
    self.fs.CreateFile('/test/text.txt')
    self.assertEqual(len(list(scandir('/test'))), 1)

This results in the following error:

ERROR: test_scandir_backport (example_test.TestExample)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/oskar/git/pyfakefs/example_test.py", line 152, in test_scandir_backport
OSError: [Errno 2] No such file or directory: '/test'

[mrbean-bremen]

Ok, I will check this tomorrow, if I find the time.

[mrbean-bremen]

Ok, several things here:

• the from scandir import scandir will generally not work under pyfakefs, you have to import scandir (there is the possibility to enable the dynamic patcher to fix this, but this is experimental and breaks at least pytest)
• the example will not work that way - you have to add the tested code to the "sut", which is example.py; I adapted the existing example to also work with the scandir module
• there was a syntax error in the other test, which I did not catch, because I tested under Windows, where the test was disabled (I overlooked this)
• there was a real bug in the implementation - it did not work under Python 2 due to changed syntax for next in the iterator (__next__ vs next)

[OskarPersson]

From my tests this seems to work now, thanks!

[mrbean-bremen]

Glad to hear that!