[docs] [issue26303] Shared execution context between doctests in a module

Feb. 6, 2016

      New submission from kernc:

The doctest execution context documentation [0] says the tests get shallow *copies* of module's globals, so one test can't mingle with results of another. This makes it impossible to make literate modules such as:

    """
    This module is about reusable doctests context.

    Examples
    --------
    Let's prepare something the later examples can work with:

    >>> import foo
    >>> result = foo.Something()
    2

    """
    class Bar:
        """
        Class about something.

        >>> bar = Bar(foo)
        >>> bar.uses(foo)
        True

        """
        def baz(self):
            """
            Returns 3.

            >>> result + bar.baz()
            5

            """
            return 3

I.e. one has to instantiate everything in every single test. The documentation says one can pass their own globals as `glob=your_dict`, but it doesn't mention the dict is *cleared* after the test run.

Please acknowledge the use case of doctests in a module sharing their environment and results sometimes legitimately exists, and to make it future-compatible, please amend the final paragraph of the relevant part of documentation [0] like so:

    You can force use of your own dict as the execution context by 
    passing `globs=your_dict` to `testmod()` or `testfile()` instead, 
    e.g., to have all doctests in a module use the _same_ execution
    context (sharing variables), define a context like so:

        class Context(dict):
            def copy(self):
                return self
            def clear(self):
                pass

    and use it, optionally prepopulated with `M`'s globals:

        doctest.testmod(module,
                        glob=Context(module.__dict__.copy()))

Thank you!

[0]: https://docs.python.org/3/library/doctest.html#what-s-the-execution-context

----------
assignee: docs@python
components: Documentation
messages: 259731
nosy: docs@python, kernc
priority: normal
severity: normal
status: open
title: Shared execution context between doctests in a module
type: enhancement
versions: Python 3.6

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Python tracker <report@bugs.python.org>
<http://bugs.python.org/issue26303>
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