A brief overview of six, a module of “utilities for wrapping between Python 2 and 3,” and cross-version compatibility as a whole.

1. 2×3=6

2. six
• Utilities for wrapping between Python 2 and 3
• Multiplication is more powerful
• “Five” has already been snatched away by the
Zope Five project
http://pythonhosted.org/six/

3. Use Case: Reflection

4. Python 2
>>> text = 'Lorem ipsum'!
>>> isinstance(text, str)!
True

5. Python 2
>>> text = u'Lorem ipsum'!
>>> isinstance(text, str)!
False

6. Python 2
>>> text = u'Lorem ipsum'!
>>> isinstance(text, str)!
False!
>>> isinstance(text, unicode)!
True

7. Python 2
>>> text1 = 'Lorem ipsum'!
>>> text2 = u'Lorem ipsum'!
>>> isinstance(text1, (str, unicode))!
True!
>>> isinstance(text2, (str, unicode))!
True

8. Python 2
>>> text1 = 'Lorem ipsum'!
>>> text2 = u'Lorem ipsum'!
>>> isinstance(text1, basestring)!
True!
>>> isinstance(text2, basestring)!
True

9. Python 3
>>> text = 'Lorem ipsum'
>>> isinstance(text, str)!
True
# "Unicode"!

10. Python 3
>>> text = u'Lorem ipsum' ! # Python 3.3+!
!
>>> isinstance(text, unicode)!
Traceback (most recent call last):!
File "<stdin>", line 2, in <module>!
NameError: name 'unicode' is not defined

11. Python 3
>>> text = 'Lorem ipsum'!
>>> isinstance(text, basestring)!
Traceback (most recent call last):!
File "<stdin>", line 2, in <module>!
NameError: name 'basestring' is not defined

12. six
>>> import six!
>>> text = 'Lorem ipsum'!
>>> isinstance(text, six.string_types)!
True!
>>> text = u'Lorem ipsum' # Python 3.3+!
>>> isinstance(text, six.string_types)!
True

13. six
Python 2
Python 3
class_types
type, types.ClassType
type
integer_types
long, int
int
string_types
basestring
str
text_type
unicode
str
binary_type
str, bytes (2.7)
bytes
MAXSIZE
sys.maxsize (2.6+)
sys.maxsize

14. Use Case:
Syntax Compatibility

15. Python 2
>>> lv = {}!
>>> exec 'x = 3, y = 4' in {}, lv!
>>> with open('foo.txt', 'w') as f:!
...
print >>f lv['x'], lv['y']!
...!
>>>

16. Python 3
>>> lv = {}!
>>> exec('x = 3, y = 4', {}, lv)!
>>> with open('foo.txt', 'w') as f:!
...
print(lv['x'], lv['y'], file=f)!
...!
>>>

17. six
>>> from six import exec_, print_!
>>> lv = {}!
>>> exec_('x = 3, y = 4', {}, lv)!
>>> with open('foo.txt', 'w') as f:!
...
print_(lv['x'], lv['y'], file=f)!
...!
>>>

18. Python 2
class MetaFoo(type):!
pass!
!
class Foo(object):!
__metaclass__ = MetaFoo

19. Python 3
class MetaFoo(type):!
pass!
!
class Foo(object, metaclass=MetaFoo):!
pass

20. six
from six import add_metaclass!
!
class MetaFoo(type):!
pass!
!
@add_metaclass(MetaFoo)!
class Foo(object):!
pass

21. six
from six import with_metaclass!
!
class MetaFoo(type):!
pass!
!
class Foo(with_metaclass(object, MetaFoo)):!
pass

22. six
Python 2
Python 3
exec_
exec (statement)
exec (function)
print_
print (statement)
print (function)
reraise
exception re-raising
(can contain previous tracebacks)
with_metaclass
metaclassing
(creates an intermediate class)
add_metaclass
metaclassing
(no intermediate class)

23. Use Case: Texts

24. Python 2
a_byte_string = 'Lorem ipsum'!
still_bytestr = b'Lorem ipsum'
a_unicode_obj = u'Lorem ipsum'
# 2.7!

25. Python 3
a_unicode_obj = 'Lorem ipsum'!
still_unicode = u'Lorem ipsum'
a_byte_string = b'Lorem ipsum'
# 3.3+ !

26. six
from six import b, u!
a_byte_string = b('Lorem ipsum')!
a_unicode_obj = u('Lorem ipsum')

27. six
a_unicode_obj = u('Lorem ipsum')
Be careful with this on Python 2!

28. six
Python 2
Python 3
b
str, bytes (2.7)
bytes
u
unicode
(allows escaping)
str
unichr
unichr
chr
int2byte
chr
bytes([integer])
byte2int
ord(bytestr[0])
bytestr[0]

29. six
Python 2
Python 3
indexbytes(buf, i)
ord(buf[i])
buf[i]
iterbytes(buf)
an iterator for a bytes instance buf
StringIO
StringIO.StringIO
io.StringIO
BytesIO
StringIO.StringIO
io.BytesIO

30. Use Case:
Name Changes

31. Python 2
from itertools import izip!
!
u = raw_input()!
!
for i, v in izip(xrange(len(u)), u):!
print i, v

32. Python 3
u = input()!
!
for i, v in zip(range(len(u)), u):!
print i, v

33. six
from six.moves import input, zip, range!
!
u = input()!
!
for i, v in zip(range(len(u)), u):!
print i, v

34. Caveats
from six.moves import ConfigParser!
!
# This will fail on Python 3!!
parser = ConfigParser.SafeConfigParser()

35. Read the Doc
(Too many to list)
http://pythonhosted.org/six/#module-six.moves

36. Advanced Usage
• Customised renames
• Object model compatibility
• six.PY2 and six.PY3 (when all others fail)

37. In the Meantime
• pies
• Supports 2.6+ only (six supports 2.4+)
• Lightweight
• python-future
• Based on six
• Let you write in pure Python 3

38. Related Reading
http://pythonhosted.org/six/
http://python3porting.com/differences.html
http://docs.python.org/3/library/
http://docs.python.org/2/library/
http://python-future.org
https://github.com/timothycrosley/pies