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Test-driven source code search for Python.

Project Description

pytest-nodev is a simple test-driven search engine for Python code, it finds classes and functions that match the behaviour specified by the given tests.

How does “test-driven code search” work?

To be more precise pytest-nodev is a pytest plugin that lets you execute a set of tests that specify the expected behaviour of a class or a function on all objects in the Python standard library and in all the modules you have installed.

Show me how it works in practice. I need to write a parse_bool function that robustly parses a boolean value from a string. Here is the test I intend to use to validate my own implementation once I write it:

def test_parse_bool():
    assert not parse_bool('false')
    assert not parse_bool('FALSE')
    assert not parse_bool('0')

    assert parse_bool('true')
    assert parse_bool('TRUE')
    assert parse_bool('1')

First, install the latest version of pytest-nodev from the Python Package Index:

$ pip install pytest-nodev

Then copy your specification test to the file and decorate it with pytest.mark.candidate as follows:

import pytest

def test_parse_bool():
    assert not parse_bool('false')
    assert not parse_bool('FALSE')
    assert not parse_bool('0')

    assert parse_bool('true')
    assert parse_bool('TRUE')
    assert parse_bool('1')

Finally, instruct pytest to run your test on all candidate callables in the Python standard library:

$ py.test --candidates-from-stdlib
======================= test session starts ==========================
platform darwin -- Python 3.5.1, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
rootdir: /tmp, inifile: setup.cfg
plugins: nodev-1.0.0, timeout-1.0.0
collected 4000 items xxxxxxxxxxxx[...]xxxxxxxxXxxxxxxxx[...]xxxxxxxxxxxx

====================== pytest_nodev: 1 passed ========================[distutils.util:strtobool] PASSED

=== 3999 xfailed, 1 xpassed, 260 pytest-warnings in 75.38 seconds ====

In just over a minute pytest-nodev collected 4000 functions from the standard library, run your specification test on all of them and reported that the strtobool function in the distutils.util module is the only candidate that passes your test.

Now you can review it and if you like it you may use it in your code. No need to write your own implementation!

Wow! Does it work so well all the times?

To be honest strtobool is a little known gem of the Python standard library that is just perfect for illustrating all the benefits of test-driven code search. Here are some of them in rough order of importance:

  • a function imported is a one less function coded—and tested, documented, debugged, ported, maintained…
  • it’s battle tested code—lot’s of old bugs have already been squashed
  • it’s other people code—there’s an upstream to report new bugs to
  • it gives you additional useful functionality—for free on top of that
  • it’s in the Python standard library—no additional dependency required


Searching code with pytest-nodev looks very much like running arbitrary callables with random arguments. A lot of functions called with the wrong set of arguments may have unexpected consequences ranging from slightly annoying, think os.mkdir('false'), to utterly catastrophic, think shutil.rmtree('/', True). Serious use of pytest-nodev, in particular using --candidates-from-all, require running the tests with operating-system level isolation, e.g. as a dedicated user or even better inside a dedicated container. The Starter kit guide documents how to run pytest-nodev safely and efficiently.

Project resources

Discussion To be decided, see issue #15
Code quality


Contributions are very welcome. Please see the CONTRIBUTING document for the best way to help. If you encounter any problems, please file an issue along with a detailed description.





pytest-nodev is free and open source software distributed under the terms of the MIT license.

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