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.. _futurize_cheatsheet:
``futurize`` quick-start guide
------------------------------
How to convert Py2 code to Py2/3 code using ``futurize``:
.. _porting-setup:
Step 0: setup
~~~~~~~~~~~~~
Step 0 goal: set up and see the tests passing on Python 2 and failing on Python 3.
a. Clone the package from github/bitbucket. Optionally rename your repo to ``package-future``. Examples: ``reportlab-future``, ``paramiko-future``, ``mezzanine-future``.
b. Create and activate a Python 2 conda environment or virtualenv. Install the package with ``python setup.py install`` and run its test suite on Py2.7 (e.g. ``python setup.py test`` or ``py.test``)
c. Optionally: if there is a ``.travis.yml`` file, add Python version 3.6 and remove any versions < 2.6.
d. Install Python 3 with e.g. ``sudo apt-get install python3``. On other platforms, an easy way is to use `Miniconda <http://repo.continuum.io/miniconda/index.html>`_. Then e.g.::
conda create -n py36 python=3.6 pip
.. _porting-step1:
Step 1: modern Py2 code
~~~~~~~~~~~~~~~~~~~~~~~
The goal for this step is to modernize the Python 2 code without introducing any dependencies (on ``future`` or e.g. ``six``) at this stage.
**1a**. Install ``future`` into the virtualenv using::
pip install future
**1b**. Run ``futurize --stage1 -w *.py subdir1/*.py subdir2/*.py``. Note that with
recursive globbing in ``bash`` or ``zsh``, you can apply stage 1 to all source files
recursively with::
futurize --stage1 -w .
**1c**. Commit all changes
**1d**. Re-run the test suite on Py2 and fix any errors.
See :ref:`forwards-conversion-stage1` for more info.
Example error
*************
One relatively common error after conversion is::
Traceback (most recent call last):
...
File "/home/user/Install/BleedingEdge/reportlab/tests/test_encrypt.py", line 19, in <module>
from .test_pdfencryption import parsedoc
ValueError: Attempted relative import in non-package
If you get this error, try adding an empty ``__init__.py`` file in the package
directory. (In this example, in the tests/ directory.) If this doesn’t help,
and if this message appears for all tests, they must be invoked differently
(from the cmd line or e.g. ``setup.py``). The way to run a module inside a
package on Python 3, or on Python 2 with ``absolute_import`` in effect, is::
python -m tests.test_platypus_xref
(For more info, see `PEP 328 <http://www.python.org/dev/peps/pep-0328/>`_ and
the `PEP 8 <http://www.python.org/dev/peps/pep-0008/>`_ section on absolute
imports.)
.. _porting-step2:
Step 2: working Py3 code that still supports Py2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The goal for this step is to get the tests passing first on Py3 and then on Py2
again with the help of the ``future`` package.
**2a**. Run::
futurize --stage2 myfolder1/*.py myfolder2/*.py
You can view the stage 2 changes to all Python source files recursively with::
futurize --stage2 .
To apply the changes, add the ``-w`` argument.
This stage makes further conversions needed to support both Python 2 and 3.
These will likely require imports from ``future`` on Py2 (and sometimes on Py3),
such as::
from future import standard_library
standard_library.install_aliases()
# ...
from builtins import bytes
from builtins import open
from future.utils import with_metaclass
Optionally, you can use the ``--unicode-literals`` flag to add this import to
the top of each module::
from __future__ import unicode_literals
All strings in the module would then be unicode on Py2 (as on Py3) unless
explicitly marked with a ``b''`` prefix.
If you would like ``futurize`` to import all the changed builtins to have their
Python 3 semantics on Python 2, invoke it like this::
futurize --stage2 --all-imports myfolder/*.py
**2b**. Re-run your tests on Py3 now. Make changes until your tests pass on Python 3.
**2c**. Commit your changes! :)
**2d**. Now run your tests on Python 2 and notice the errors. Add wrappers from
``future`` to re-enable Python 2 compatibility. See the
:ref:`compatible-idioms` cheat sheet and :ref:`what-else` for more info.
After each change, re-run the tests on Py3 and Py2 to ensure they pass on both.
**2e**. You're done! Celebrate! Push your code and announce to the world! Hashtags
#python3 #python-future.
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