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A rewrite of the builtin doctest module

Project description

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The xdoctest package is a re-write of Python’s builtin doctest module. It replaces the old regex-based parser with a new abstract-syntax-tree based parser (using Python’s ast module). The goal is to make doctests easier to write, simpler to configure, and encourage the pattern of test driven development.

Read the docs
PyCon 2020 Youtube Video and Google Slides

Quick Start

Installation: from pypi

Xdoctest is distributed on pypi as a universal wheel and can be pip installed on Python 2.7, Python 3.4+. Installations are tested on CPython and PyPy implementations.

pip install xdoctest

Distributions on pypi are signed with a GPG public key: D297D757. If you care enough to check the gpg signature (hopefully pip will just do this in the future), you should also verify this agrees with the contents of dev/public_gpg_key.

Usage: Run your Doctests

After installing, the fastest way to run all doctests in your project is:

python -m xdoctest /path/to/your/

or if your module has been pip-installed / is in the PYTHONPATH run

python -m xdoctest yourmodname

Getting Started

There are two ways to use xdoctest: via pytest or via the native interface. The native interface is less opaque and implicit, but its purpose is to run doctests. The other option is to use the widely used pytest package. This allows you to run both unit tests and doctests with the same command and has many other advantages.

It is recommended to use pytest for automatic testing (e.g. in your CI scripts), but for debugging it may be easier to use the native interface.

Check if xdoctest will work on your package

You can quickly check if xdoctest will work on your package out-of-the box by installing it via pip and running python -m xdoctest <pkg> all, where <pkg> is the path to your python package / module (or its name if it is installed in your PYTHONPATH).

For example with you might test if xdoctest works on networkx or sklearn as such: python -m xdoctest networkx all / python -m xdoctest sklearn all.

Using the pytest interface

When pytest is run, xdoctest is automatically discovered, but is disabled by default. This is because xdoctest needs to replace the builtin doctest plugin.

To enable this plugin, run pytest with --xdoctest or --xdoc. This can either be specified on the command line or added to your addopts options in the [pytest] section of your pytest.ini or tox.ini.

To run a specific doctest, xdoctest sets up pytest node names for these doctests using the following pattern: <path/to/>::<callname>:<num>. For example a doctest for a function might look like this, and a class method might look like this:

Using the native interface.

The xdoctest module contains a pytest plugin, but also contains a native interface. This interface is run programmatically using xdoctest.doctest_module(path), which can be placed in the __main__ section of any module as such:

if __name__ == '__main__':
    import xdoctest as xdoc

This sets up the ability to invoke the xdoctest command line interface. python -m <modname> <command>

  • If <command> is all, then each enabled doctest in the module is executed: python -m <modname> all
  • If <command> is list, then the names of each enabled doctest is listed.
  • If <command> is dump, then all doctests are converted into a format suitable for unit testing, and dumped to stdout (new in 0.4.0).
  • If <command> is a callname (name of a function or a class and method), then that specific doctest is executed: python -m <modname> <callname>. Note: you can execute disabled doctests or functions without any arguments (zero-args) this way.

For example if you created a module with the following code:

def func1():
        >>> assert func1() == 1
    return 1

def func2(a):
        >>> assert func2(1) == 2
        >>> assert func2(2) == 3
    return a + 1

if __name__ == '__main__':
    import xdoctest as xdoc

You could

  • Use the command python -m mymod list to list the names of all functions with doctests
  • Use the command python -m mymod all to run all functions with doctests
  • Use the command python -m mymod func1 to run only func1’s doctest
  • Use the command python -m mymod func2 to run only func2’s doctest

Lastly, by running the command xdoc.doctest_module(<pkgname>), xdoctest will recursively find and execute all doctests within the modules belonging to the package.

Zero-args runner

A benefit of using the native interface is the “zero-args” mode in the xdoctest runner. This allows you to run functions in your modules via the command line as long as they take no arguments. The purpose is to create a quick entry point to functions in your code (because xdoctest is taking the space in the __main__ block).

For example, you might create a module with the following code:

def myfunc():
    print('hello world')

if __name__ == '__main__':
    import xdoctest as xdoc

Even though myfunc has no doctest it can still be run using the command python -m mymod myfunc.

Note, even though “zero-arg” functions can be run via this interface they are not run by python -m mymod all, nor are they listed by python -m mymod list.


The main enhancements xdoctest offers over doctest are:

  1. All lines in the doctest can now be prefixed with >>>. There is no need for the developer to differentiate between PS1 and PS2 lines. However, old-style doctests where PS2 lines are prefixed with ... are still valid.
  2. Additionally, the multi-line strings don’t require any prefix (but its ok if they do have either prefix).
  3. Tests are executed in blocks, rather than line-by-line, thus comment-based directives (e.g. # doctest: +SKIP) are now applied to an entire block, rather than just a single line.
  4. Tests without a “want” statement will ignore any stdout / final evaluated value. This makes it easy to use simple assert statements to perform checks in code that might write to stdout.
  5. If your test has a “want” statement and ends with both a value and stdout, both are checked, and the test will pass if either matches.
  6. Ouptut from multiple sequential print statements can now be checked by a single “got” statement. (new in 0.4.0).

See code in _compare/ and _compare/ for a demo that illustrates several of these enhancements. This demo mostly shows cases where xdoctest works but doctest fails, but it does show the only corner case I can find where doctest works but xdoctest does not. Feel free to submit more in an issue if you can find any other backwards incompatible cases.


Here is an example demonstrating the new relaxed (and backwards-compatible) syntax:

def func():
    # Old way
    >>> def func():
    ...     print('The old regex-based parser required specific formatting')
    >>> func()
    The old regex-based parser required specific formatting

    # New way
    >>> def func():
    >>>     print('The new ast-based parser lets you prefix all lines with >>>')
    >>> func()
    The new ast-based parser lets you prefix all lines with >>>
def func():
    # Old way
    >>> print('''
    ... It would be nice if we didnt have to deal with prefixes
    ... in multiline strings.
    ... '''.strip())
    It would be nice if we didnt have to deal with prefixes
    in multiline strings.

    # New way
    >>> print('''
        Multiline can now be written without prefixes.
        Editing them is much more natural.
    Multiline can now be written without prefixes.
    Editing them is much more natural.

    # This is ok too
    >>> print('''
    >>> Just prefix everything with >>> and the doctest should work
    >>> '''.strip())
    Just prefix everything with >>> and the doctest should work


Google style doctest support

Additionally, this module is written using Google-style docstrings, and as such, the module was originally written to directly utilize them. However, for backwards compatibility and ease of integration into existing software, the pytest plugin defaults to using the more normal “freestyle” doctests that can be found anywhere in the code.

To make use of Google-style docstrings, pytest can be run with the option --xdoctest-style=google, which causes xdoctest to only look for doctests in Google “docblocks” with an Example: or Doctest: tag.

Notes on Got/Want tests

The new got/want tester is very permissive by default; it ignores differences in whitespace, tries to normalize for python 2/3 Unicode/bytes differences, ANSI formatting, and it uses the old doctest ELLIPSIS fuzzy matcher by default. If the “got” text matches the “want” text at any point, the test passes.

Currently, this permissiveness is not highly configurable as it was in the original doctest module. It is an open question as to whether or not this module should support that level of configuration. If the test requires a high degree of specificity in the got/want checker, it may just be better to use an assert statement.

Backwards Compatibility

We (I) have removed all known backwards syntax incompatibilities. This is based on running doctests on real life examples: boltons, ubelt, networkx, pytorch (pending their acceptance of a pull-request), and on a set of extensive self-testing. Please raise an issue or submit a merge/pull request.

Despite full syntax backwards compatibility, there are directive incompatibilities by design. The directives we expose are more consise and expressive. Our “got”/”want” checker is also much more permissive. We recommend that you rely on coded assert-statements for system-critical code. This also makes it much easier to transform your xdoctest into a unittest when you realize your doctests start getting too long.

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