difference between __repr__() and __str__()

[Gregoire Welraeds]

The question is in the subject. According to the Python reference manual,
page 17 

__repr__: called to compute the official string representation of an
object. This should like a valid Python expression that can be used to
recreate an object with the same value.

__str__: differs from repr in that in does not have to be a valid python
expression: a more conveniant or concise representation maybe used
instead.

What is a valid Python expression ?
I though that repr was called by repr and by string conversion (as
mentionned early in the doc)not to recreate an object ?
What is the use of an official string representation against the
non-official ? 

--
Life is not fair
But the root password helps
--

Gregoire Welraeds
greg at perceval.be
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