python3: tests collecting fails with TypeError: object of type 'map' has no len()

[lpramuk]

$ py.test --collect-only -v tests/foreman/cli/test_setting.py
================================================= test session starts ==================================================
platform linux -- Python 3.6.4, pytest-3.4.2, py-1.5.2, pluggy-0.6.0 -- /home/jenkins/shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/bin/python3.6
cachedir: .pytest_cache
shared_function enabled - OFF - scope:  - storage: file
rootdir: /home/jenkins/workspace/automation-6.3-tier1-rhel7, inifile:
plugins: xdist-1.22.2, services-1.2.1, mock-1.6.3, forked-0.2
collected 0 items / 1 errors                                                                                           
2018-03-21 05:59:18 - conftest - DEBUG - Collected 0 test cases


======================================================== ERRORS ========================================================
__________________________________ ERROR collecting tests/foreman/cli/test_setting.py __________________________________
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/pluggy/__init__.py:617: in __call__
    return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/pluggy/__init__.py:222: in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/pluggy/__init__.py:216: in <lambda>
    firstresult=hook.spec_opts.get('firstresult'),
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/_pytest/python.py:200: in pytest_pycollect_makeitem
    res = list(collector._genfunctions(name, obj))
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/_pytest/python.py:378: in _genfunctions
    self.ihook.pytest_generate_tests(metafunc=metafunc)
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/pluggy/__init__.py:617: in __call__
    return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/pluggy/__init__.py:222: in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/pluggy/__init__.py:216: in <lambda>
    firstresult=hook.spec_opts.get('firstresult'),
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/_pytest/python.py:125: in pytest_generate_tests
    metafunc.parametrize(*marker.args, **marker.kwargs)
../../shiningpanda/jobs/375dbdea/virtualenvs/d41d8cd9/lib/python3.6/site-packages/_pytest/python.py:824: in parametrize
    if len(ids) != len(parameters):
E   TypeError: object of type 'map' has no len()
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
================================================== 0 tests deselected ==================================================
=============================================== 1 error in 0.68 seconds ================================================

There is one test that cause collector to fail on python3:

@pytest.mark.parametrize('value', **xdist_adapter(invalid_boolean_strings()))
def test_negative_update_send_welcome_email(value):

Collector is not python3 ready as it fails when collecting tests with the following mark @pytest.mark.parametrize()

[lpramuk]

In python3 you can't do:

len(map(lambda x: x, [1,3,5,7]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'map' has no len()

the fix is to convert map into a list:

>>> len(list(map(lambda x: x, [1,3,5,7])))
4

[pytestbot]

GitMate.io thinks possibly related issues are #638 (python.py:813 (in "parametrize") raises "TypeError: object of type 'int' has no len()" in some cases), #651 (test fails in ntpath.py when LocalPath has no len), #747 (flakes test fail), #1777 (sigalrm fails test), and #239 (not collect deselected tests).

[The-Compiler]

I don't think passing anything other than a sequence to parametrize is supported by pytest.

[lpramuk]

I can submit PR, there are just two occurences to fix:
https://github.com/pytest-dev/pytest/blob/master/_pytest/python.py#L824
https://github.com/pytest-dev/pytest/blob/master/_pytest/python.py#L952

[lpramuk]

RE passing anything other than a sequence to parametrize

Why then with python2.7 there is no problem to collect such tests?

[The-Compiler]

Trying to "fix" this in pytest will probably have wider implications - you should really just use the pytest API like documented, which means passing a list (or at least some kind of sequence) to pytest.

Why then with python2.7 there is no problem to collect such tests?

Because map returns a list in Python 2.

[lpramuk]

Ok we can fix it then probably ourselves by changing map to list in our code. Yay

[RonnyPfannschmidt]

note that both points in pytest would fix it wrong and break on marker reuse and/or double call

[RonnyPfannschmidt]

but we should probably assert that we get an actual sequence there,

[lpramuk]

Thanks guys I'm happy with closing this issue now