Add methods to a class at runtime?

[Gerhard Häring]

Robert Oschler wrote in comp.lang.python:
> [Glyph said:]
> "One of the eye-popping cool features of Python is the ability to
> change code and have existing instances update to use the new
> methods automatically. "
> 
> Can someone point me to a code snippet shows how to do this?

>>> class Foo: pass
... 
>>> foo = Foo()
>>> foo.bar()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: Foo instance has no attribute 'bar'
>>> def bar(self): print "bar"
... 
>>> Foo.bar = bar
>>> foo.bar()
bar
>>> 
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reduce(lambda x,y:x+y,map(lambda x:chr(ord(x)^42),tuple('zS^BED\nX_FOY\x0b')))