We wish to maintain a single-source codebase that is Python 2/3 compatible. Modules such as futurize and modernize are helpful but moving forward, we want to write futurized and compatible code.

Basic functionalities

  • Include this in the python header or template file so that it is automatically included everytime a .py file is created.
from __future__ import print_function
from __future__ import division
from __future__ import absolute_import
from __future__ import unicode_literals
  • Write print functions as print("Something")
  • Format print functions with print("Something {}".format('!'))
  • Import custom modules as from . import mymodule

Dealing with exceptions

  • Raising exceptions is raise "Your useful error message" in python2 but should be written as raise Exception("Your useful error message")

Text versus binary

  • Handle binary and text with edge code (reading in and writing out) that decodes and encodes binary data. str in python2 was a valid type for both text and binary data, but python3 makes the distinction clear with str for text and bytes for binary.
with open('somefile.txt', 'r') as f:
  text = f.readlines()
with open('somefile', 'rb') as f:
  binary = f.read()

text = binary.decode('utf-8')
binary = text.encode('utf-8')
  • Do not use unicode type, instead just use str. unicode in python2 was a valid type for unicode but does not exist in python3.

Inbuilt dictionary

  • In python2 we could examine the value of the dictionary with dict[dict.keys()[0]]. However python3 dict.keys() returns a non-indexable iterable.
  • Get arbitary key of dictionary with list(dict.keys())[0]
  • Get arbitary item of dictionary with list(dict.values)[0]
    Indexing at 0 is arbitary because python dictionaries are unordered.

Library dependencies

  • cPickle in python2 is now _pickle in python3
  • importlib in python2 is now importlib2 in python3
  import cPickle as pickle
  import _pickle as pickle

Bonus Stuff

  • Use generator comprehensions instead of list comprehensions if performing operations on the sequence. sum(x for x in xrange(100000))
  • This is both more time ans space efficient especially on huge lists. Both list and generator are compatible in both python2 and 3.


90% of this is written from own experience. For a better understanding on testing, packaging code and other software-engineering oriented practices, best to consult the official docs.