Command-line/Web Usage

You can specify your dependencies in multiple ways:

caniusepython3 -r requirements.txt test-requirement.txt
caniusepython3 -m PKG-INFO
caniusepython3 -p numpy scipy ipython
# If your project's setup.py uses setuptools
# (note that setup_requires can't be checked) ...
python setup.py caniusepython3

The output of the script will tell you how many (implicit) dependencies you need to transition to Python 3 in order to allow you to make the same transition. It will also list what projects have no dependencies blocking their transition so you can ask them to start a port to Python 3.

If you prefer a web interface you can use https://caniusepython3.com by Jannis Leidel.

Integrating With Your Tests

If you want to check for Python 3 availability as part of your tests, you can use caniusepython3.check():

def check(requirements_paths=[], metadata=[], projects=[]):
    """Return True if all of the specified dependencies have been ported to Python 3.

    The requirements_paths argument takes a sequence of file paths to
    requirements files. The 'metadata' argument takes a sequence of strings
    representing metadata. The 'projects' argument takes a sequence of project
    names.

    Any project that is not listed on PyPI will be considered ported.
    """

You can then integrate it into your tests like so:

import unittest
import caniusepython3

class DependenciesOnPython3(unittest.TestCase):
  def test_dependencies(self):
    # Will begin to fail when dependencies are no longer blocking you
    # from using Python 3.
    self.assertFalse(caniusepython3.check(projects=['ipython']))

For the change log, how to tell if a project has been ported, as well as help on how to port a project, please see the project website.

Extending pylint --py3k

In Pylint 1.4, a --py3k option was added to the linting tool to turn on checks for Python 2/3 incompatibilities (all other checks are turned off). While great, those checks are a little conservative in order to always be accurate. To fill out those checks with stricter – albeit potentially inaccurate – checkers, caniusepython3.pylint_checker exists. On top of everything pylint --py3k already checks for, it adds checks for:

1. Uses of open() (in Python3, open() is actually io.open())
2. String literals that do not have a b/u prefix or from __future__ import unicode_literals

If you wish to use the checker with Pylint, you can add it to your Pylint configuration file, e.g.:

[MASTER]
load-plugins=caniusepython3.pylint_checker

Secret, bonus feature

If you would like to use a different name for the script and setuptools command then set the environment variable CIU_ALT_NAME to what you would like the alternative name to be. Reddit suggests icanhazpython3.