Short confusing example with unicode, print, and __str__

[Gerard Brunick]

I really don't understand the following behavior:

 >>> class C(object):
...     def __init__(self, s): self.s = s
...     def __str__(self): return self.s
...
 >>> cafe = unicode("Caf\xe9", "Latin-1")
 >>> c = C(cafe)
 >>> print "Print using c.s:", c.s
Print using c.s: Café
 >>> print "Print using just c:", c
Print using just c: Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in 
position 3: ordinal not in range(128)
 >>> str(c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in 
position 3: ordinal not in range(128)

Why would "print c.s" work but the other two cases throw an exception?
Any help understanding this would be greatly appreciated.

Thanks in advance,
Gerard