Using __repr__ or __str__ for own printable class?

Steven Taschuk staschuk at telusplanet.net
Thu Apr 17 04:37:38 CEST 2003


Quoth Peter Hansen:
  [...]
> I've always considered __repr__ to be for use in *debugging* the
> application, where a *debugging* log needs to display information,
> or in a traceback.  Since it's next to impossible for most interesting
> objects to be reproduced easily from the output of __repr__ if it's
> also desirable that the output be meaningful and useful to a human 
> reader, I don't buy into the 'eval(repr(x)) == x' theory very much,
> other than to note that it's the most obvious thing to do for 
> primitive data types.

There are, I admit, lots of objects for which the eval(repr(x)) ==
x theory doesn't make sense.  (File objects, for example.)  But in
my (admittedly not very broad) experience, these tend to be
objects for which == doesn't make sense in the first place.

Imho the notion that eval(repr(x)) == x theory makes lots of sense
for value objects generally.  (See, e.g., the timbot's example of
datetime.date.)

> I've never had any confusion in my own mind about when it's 
> appropriate to use one or the other.  Perhaps this perspective 
> should be used in the documentation, rather than the focus on 
> reproducing objects from their __repr__.  

*shrug*  As quoted in another post, the docs explicitly state that
repr "is typically used for debugging".  I suppose it could be
more emphasized.

-- 
Steven Taschuk                                                   w_w
staschuk at telusplanet.net                                      ,-= U
                                                               1 1





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