Create unicode string "a".

>>> a = u'\u2019'
>>> a
u'\u2019'

Convert to ASCII string (ASCII is default for Python 2 str()).

>>> str(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2019' in position 0: ordinal not in range(128)

Encode the unicode string to UTF-8 (overriding the default of ASCII).

>>> str(a.encode('utf-8'))
'\xe2\x80\x99'
>>> print str(a.encode('utf-8'))
’

For a greater understanding, see Ned Batchelder's great "Pragmatic Unicode, or, How do I stop the pain?" (2012) video.