Untitled

.py

# encoding: utf-8
name = 'helló wörld from two'

# encoding: utf-8
from __future__ import unicode_literals
import two
name = 'helló wörld from one'
print name + two.name

Traceback (most recent call last):
  File "one.py", line 5, in <module>
    print name + two.name
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 4: ordinal not in range(128)

# encoding: utf-8
html = '<html><body>helló wörld</body></html>'
if isinstance(html, unicode):
    html = html.encode('utf-8')
print 'DEBUG: %s' % html

DEBUG: <html><body>helló wörld</body></html>

# encoding: utf-8
from __future__ import unicode_literals
html = '<html><body>helló wörld</body></html>'
if isinstance(html, unicode):
    html = html.encode('utf-8')
print 'DEBUG: %s' % html

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    print 'DEBUG: %s' % html
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 16: ordinal not in range(128)

>>> def foo(a=None): pass
  ...
  >>> foo(**{'a':1})
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
      TypeError: foo() keywords must be strings

# -*- coding: utf-8

foo = "barré"

unicode_literal

from __future__ import unicode_literals

bstr = b'xa4'
assert eval(repr(bstr)) == bstr # fails in Python 2.7, holds in 3.1

ustr = 'xa4'
assert eval(repr(bstr)) == bstr # holds in Python 2.7 and 3.1