2 + 3 - 6

Why?

• Because I'm Lazy (remember, this is a Good Thing)
• 2to3 is okay, but fails in a few annoying ways
• Six is okay, but adds something I'll only have to remove later

How? (non-code bits)

1. Give up on compatibility with Python < 2.6
2. It's not horribly unreasonable (2.6 or above is now default on most common platforms)

How? (code bits)

1. Add a full complement of from __future__ imports to all your modules
2. Make all strings compatible (u'' to '')
3. Make all print statements functions (print '' to print(''))
4. Make all relative imports absolute (you were using relative imports? Tut tut)
5. Grep for any division operators and check their type

Example

from __future__ import (
    unicode_literals,
    print_function,
    absolute_import,
    division,
    )

from rastools.raspase import RasParser
# ^--- absolute import

print('Some stuff')
# ^--- using print function

What Next?

• Test with a python2 virtualenv sandbox
• Test with a python3 virtualenv sandbox
• Fix stuff
• Test again
• And again...
• Repeat until you're utterly sick of testing

Stuff you'll probably find

• Import renames (yes, six is useful here - but either way you're going to have stuff to remove later)
• If you use renames yourself, choose the python 3 names (duh)
• Strings vs bytes in a few places (anything using struct?)

Example

from PIL import Image
try:
    # XXX Py2 only
    from cStringIO import StringIO
except ImportError:
    # XXX Py2 only
    from StringIO import StringIO
except ImportError:
    # XXX Py3 only
    from io import StringIO

More Examples!

try:
    self._file = open(filename_or_obj, 'w')
except TypeError:
    self._file = filename_or_obj

if isinstance(filename_or_obj, basestring):
    self._file = open(filename_or_obj, 'w')
else:
    self._file = filename_or_obj

Packaging

• Very little to do:
• Remove any 2to3 reference in setup.py
• Add a Trove classifier for Python 3
• Make a .deb (what do you mean you haven't got one?!)
• Profit!

Conclusion

• Either way you're going to have some stuff to remove later
• The trick is to keep it to a minimum
• Remember: be lazy!