In Python 2.6 a performance optimization was added to the hmac module
(http://bugs.python.org/issue1618455). This appears to have the
unintended consequence of no longer accepting unicode strings as input.

Python 2.5.1 (r251:54863, Feb  4 2008, 21:48:13) 
>>> import hmac
>>> hmac.new(u'key','msg')
<hmac.HMAC instance at 0x6e440>

Python 2.6.1 (r261:67515, Dec  9 2008, 14:49:30) 
>>> import hmac
>>> hmac.new(u'key','msg')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File
"/Users/kteague/buildouts/shared/python-2.6.1/lib/python2.6/hmac.py",
line 133, in new
    return HMAC(key, msg, digestmod)
  File
"/Users/kteague/buildouts/shared/python-2.6.1/lib/python2.6/hmac.py",
line 72, in __init__
    self.outer.update(key.translate(trans_5C))
TypeError: character mapping must return integer, None or unicode

This change is also reflected in Python 3.0 as the hmac module only
accepts data as input (althought the docs still mention 'strings').

Python 3.0.1 (r301:69556, Feb 16 2009, 14:38:14) 
>>> import hmac
>>> hmac.new('key','msg')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File
"/Users/kteague/buildouts/shared/python-3.0.1/lib/python3.0/hmac.py",
line 140, in new
    return HMAC(key, msg, digestmod)
  File
"/Users/kteague/buildouts/shared/python-3.0.1/lib/python3.0/hmac.py",
line 43, in __init__
    raise TypeError("expected bytes, but got %r" % type(key).__name__)
TypeError: expected bytes, but got 'str'
>>> hmac.new(b'key',b'msg')
<hmac.HMAC object at 0x3a1810>

This module should likely accept both string and unicode (Python 2) or
text and data (Python 3) and handle the conversion internally?

Python 3 behavior is correct.  Since HMAC operates on bytes, not text,
only bytes are accepted. In Python 2, the acceptance of Unicode strings
is more an accident than a feature.

This damn bug ruined my day. MoinMoin couldn't reset password on many outdated wikies < 1.8.2 (including Python's one probably), because of it.

http://moinmo.in/MoinMoinBugs/1.8_ResetPasswordError