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23.2.3.3 What's the Execution Context?

By default, each time `doctest` finds a docstring to test, it uses a shallow copy of `M`'s globals, so that running tests doesn't change the module's real globals, and so that one test in `M` can't leave behind crumbs that accidentally allow another test to work. This means examples can freely use any names defined at top-level in `M`, and names defined earlier in the docstring being run. Examples cannot see names defined in other docstrings.

You can force use of your own dict as the execution context by passing `globs=your_dict` to `testmod()` or `testfile()` instead.