encoding a unicode string

>>> s = u'→é'
>>> s.encode('utf-8')
'\xe2\x86\x92\xc3\xa9'
>>> s.encode('utf-16')
'\xff\xfe\x92!\xe9\x00'
>>> s.encode('ascii')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordinal not in range(128)