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A rewrite of the builtin doctest module

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Xdoctest - Execute doctests. A Python package for executing tests in documentation strings!

What is a doctest? It is example code you write in a docstring! What is a docstring? Its a string you use as a comment! They get attached to Python functions and classes as metadata. They are often used to auto-generate documentation. Why is it cool? Because you can write tests while you code!

Tests are good. Documentation is good. Examples are good. Doctests have low boilerplate, you write them in the same file you write your code. It often can help you write the function. Write down how to construct minimal demo inputs (it helps to have tools to create these) in your file. Copy that code into IPython/Jupyter, and play with your implementation. Copy your finished code into the body. Write down how to call the function with the demo inputs. If you feel inclined, check that the result matches an expected result (while asserts and checks are nice, a test that just shows how to run the code is better than no test at all).

def an_algorithm(data, config):
        >>> data = '([()[]])[{}([[]])]'
        >>> config = {'outer': sum, 'inner': ord}
        >>> an_algorithm(data, config)
    # I wrote this function by first finding some interesting demodata
    # then I wrote the body in IPython and copied it back in.
    # Now I can re-use this test code I wrote in development as a test!
    # Covered Code is much easier to debug (we have a MWE)!
    result = config['outer'](map(config['inner'], data))
    return result

The problem? How do you run the code in your doctest?

Xdoctest finds and executes your doctests for you. Just run xdoctest <path-to-my-module>. It plugs into pytest to make it easy to run on a CI. Install and run pytest --xdoctest.

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 3.6+ (Python 2.7 and 3.4 / 3.5 support was removed in Version 1.1.0). 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.

In addition to the pytest plugin, xdoctest has a native doctest runner. You can use the xdoctest command line tool that is installed with the package and point it a module directory or a particular file.

You can also make it such that invoking your module as __main__ invokes the xdoctest native runner using the using the xdoctest.doctest_module(path) method, which can be placed in the __main__ section of any module as such:

if __name__ == '__main__':
    import xdoctest

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

However, it is typically prefered to just use the xdoctest executable and pass it the path to your file, or the name of an installed module. In this case it is invoked like xdoctest -m <modname> <command>.

Using either of these methods you can natively invoke xdoctest on a module or package, which exposes the command line interface. Both of these expose the command line interface, allowing you to pass a command to xdoctest.

  • 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

You could

  • Use the command xdoctest -m mymod list to list the names of all functions with doctests

  • Use the command xdoctest -m mymod all to run all functions with doctests

  • Use the command xdoctest -m mymod func1 to run only func1’s doctest

  • Use the command xdoctest -m mymod func2 to run only func2’s doctest

Passing --help to either way of invoking the native runner will result in something similar to the following that outlines what other options are available:

usage: xdoctest [-h] [--version] [-m MODNAME] [-c COMMAND] [--style {auto,google,freeform}] [--analysis {auto,static,dynamic}] [--durations DURATIONS] [--time]
                [--colored COLORED] [--nocolor] [--offset] [--report {none,cdiff,ndiff,udiff,only_first_failure}] [--options OPTIONS] [--global-exec GLOBAL_EXEC]
                [--verbose VERBOSE] [--quiet] [--silent]
                [arg ...]

Xdoctest 1.0.1 - on Python - 3.9.9 (main, Jun 10 2022, 17:45:11)
[GCC 11.2.0] - discover and run doctests within a python package

positional arguments:
  arg                   Ignored if optional arguments are specified, otherwise: Defaults --modname to arg.pop(0). Defaults --command to arg.pop(0). (default: None)

optional arguments:
  -h, --help            show this help message and exit
  --version             Display version info and quit (default: False)
  -m MODNAME, --modname MODNAME
                        Module name or path. If specified positional modules are ignored (default: None)
  -c COMMAND, --command COMMAND
                        A doctest name or a command (list|all|<callname>). Defaults to all (default: None)
  --style {auto,google,freeform}
                        Choose the style of doctests that will be parsed (default: auto)
  --analysis {auto,static,dynamic}
                        How doctests are collected (default: auto)
  --durations DURATIONS
                        Specify execution times for slowest N tests.N=0 will show times for all tests (default: None)
  --time                Same as if durations=0 (default: False)
  --colored COLORED     Enable or disable ANSI coloration in stdout (default: True)
  --nocolor             Disable ANSI coloration in stdout
  --offset              If True formatted source linenumbers will agree with their location in the source file. Otherwise they will be relative to the doctest itself. (default:
  --report {none,cdiff,ndiff,udiff,only_first_failure}
                        Choose another output format for diffs on xdoctest failure (default: udiff)
  --options OPTIONS     Default directive flags for doctests (default: None)
  --global-exec GLOBAL_EXEC
                        Custom Python code to execute before every test (default: None)
  --verbose VERBOSE     Verbosity level. 0 is silent, 1 prints out test names, 2 additionally prints test stdout, 3 additionally prints test source (default: 3)
  --quiet               sets verbosity to 1
  --silent              sets verbosity to 0

Zero-args runner

The native interface has a “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

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.

However, if you are doing this often, you may be better served by fire.


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) can now applied to an entire block (by placing it one the line above), in addition to having it just apply to a single line (by placing it in-line at the end).

  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 dev/_compare/ for a demo that illustrates several of these enhancements. This demo shows cases where xdoctest works but doctest fails. As of version 0.9.1, there are no known syntax backwards incompatability. Please submit an issue if you can find any 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


Xdoctest Parsing Style

There are currently two main doctest parsing styles: google and freeform, as well as a third style: auto, which is a hybrid.

The parsing style can be set via the --style command line argument in the Xdoctest CLI, or via the --xdoctest-style if using pytest.

Setting --style=google (or --xdoctest-style=google in pytest) enables google-style parsing. A Google-style doctest is expected to exist in Google “docblock” with an Example: or Doctest: tag. All code in this block is parsed out as a single doctest.

Setting --style=freeform (or --xdoctest-style=freeform in pytest) enables freeform-style parsing. A freeform style doctest is any contiguous block of lines prefixed by >>>. This is the original parsing style of the builtin doctest module. Each block is listed as its own test.

By default Xdoctest sets --style=auto (or --xdoctest-style=auto in pytest) which will pull all google-style blocks out as single doctests, while still all other >>> prefixed code out as a freeform doctest.

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

There are no known syntax incompatibilities with original doctests. This is based on running doctests on real life examples in boltons, ubelt, networkx, pytorch, and on a set of extensive testing suite. Please raise an issue or submit a merge/pull request if you find any incompatibility.

Despite full syntax backwards compatibility, there some runtime incompatibilities by design. Specifically, Xdoctest enables a different set of default directives, such that the “got”/”want” checker is more permissive. Thus, a test that fails in doctest based on a “got”/”want” check, may pass in xdoctest. For this reason it is recommended 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 are getting too long.

One Last Example

XDoctest is a good demonstration of itself. After pip installing xdoctest, try running xdoctest on xdoctest.

xdoctest xdoctest

If you would like a slightly less verbose output, try

xdoctest xdoctest --verbose=1

# or

xdoctest xdoctest --verbose=0

You could also consider running xdoctests tests through pytest:

pytest $(python -c 'import xdoctest, pathlib; print(pathlib.Path(xdoctest.__file__).parent)') --xdoctest

If you would like a slightly more verbose output, try

pytest -s --verbose --xdoctest-verbose=3 --xdoctest $(python -c 'import xdoctest, pathlib; print(pathlib.Path(xdoctest.__file__).parent)')

If you ran these commands, the myriad of characters that flew across your screen are lots more examples of what you can do with doctests.

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