How can I clear/shadow globals before doctests are run?

[adeak]

The default behaviour of pytest is that doctests see the module-global namespace. This seems to correspond to stdlib doctest. I'm trying to isolate doctests from the module global namespace in order to ensure that copy-pasting doctests into a python script or REPL will work as intended. I've found the doctest_namespace fixture, but that only seems to add names rather than overwrite them.

Specific example:

$ tree
.
└── test_package
    └── foo
        ├── bar.py
        └── __init__.py

$ cat test_package/foo/bar.py 
val = 42

class Bar:
    def baz(self):
        """Use the quux.

        Examples
        --------

        >>> val == 42
        True

        """
        return True

__init__.py is empty.

In the above doctest, val is pulled in from the module global namespace so the test succeeds:

$ pytest -v --doctest-modules test_package/
=============================================================================================== test session starts ===============================================================================================
platform linux -- Python 3.9.1+, pytest-6.2.4, py-1.10.0, pluggy-0.13.1 -- /home/adeak/tmp_env/bin/python3.9
cachedir: .pytest_cache
rootdir: /home/adeak/doctest_test_dir
collected 1 item                                                                                                                                                                                                  

test_package/foo/bar.py::foo.bar.Bar.baz PASSED                                                                                                                                                             [100%]

================================================================================================ 1 passed in 0.17s ================================================================================================

I want it to fail (with a NameError), because val is not defined in the doctest itself.

How can I make the doctest fail, by effectively passing an empty dict to use as the globals() of the doctest?

[RonnyPfannschmidt]

its not effectively possible

emptying the global name-space practically would break code using the classes

same goes for using modified copies and potentially a number of other details

this should first be experimented with in a plugin to figure how to make it sensible

[adeak]

Thanks. Does this also apply if the package being tested is installed? Names would all be created from scratch.

[adeak]

The specific use case motivating my question is doctests in PyVista, for instance here:

        >>> import pyvista as pv
        >>> s1 = pv.Sphere()
        >>> s2 = pv.Sphere(center=(0.25, 0, 0))
        >>> intersection, s1_split, s2_split = s1.intersection(s2)

There is no need for module-level globals here. And if we accidentally wrote pyvista instead of pv on the middle lines, the doctest would still pass because we have pyvista in the module global namespace.

So I mean to say: when you say this would "break code using the classes", do you mean breaking pytest, or breaking the doctests themselves, or something else?

[RonnyPfannschmidt]

it would break doctests themself, a good number of them are not correctly self-contained

[adeak]

OK, thanks for the explanation and quick reply :)