On Fri, Jun 27, 2008 at 11:16:18PM +0200, Fredrik Johansson wrote:
>
> On Fri, Jun 27, 2008 at 10:56 PM, Kirill Smelkov
> <[EMAIL PROTECTED]> wrote:
>
> > I quote http://docs.python.org/ref/customization.html#l2h-183
> >
> > __repr__(self):
> >
> > Called by the repr() built-in function and by string conversions (reverse
> > quotes) to compute the ``official'' string representation of an object. If
> > at
> > all possible, this should look like a valid Python expression that could be
> > used to recreate an object with the same value (given an appropriate
> > environment). If this is not possible, a string of the form "<...some
> > useful
> > description...>" should be returned. The return value must be a string
> > object.
> > If a class defines __repr__() but not __str__(), then __repr__() is also
> > used
> > when an ``informal'' string representation of instances of that class is
> > required.
>
> Note "given an appropriate environment". The appropriate environment
> is use within SymPy so I think it is actually sufficient if
> sympify(repr(x)) == x holds, sympify taking the role of eval. It is
> fine in my opinion if repr displays rationals as 2/3, etc.
>
> > This is typically used for debugging, so it is important that the
> > representation is information-rich and unambiguous.
> >
> >
> > So, say about Symbol('x') -> 'x' -- symbols could be Dummy, Temporary, they
> > could have non-default assumption, etc.
>
> Yes, and this is something I have pointed out before. It is very
> problematic that expressions can have "hidden" properties, that don't
> show up in the output of either repr() or str(). My suggested solution
> is to remove assumptions from expressions and get rid of
> Dummy/Temporary/Wild, just having symbols.
Why woudn't str(expr) serve for this?
Guys, you are just forcing someone to invent another pairs of methods
for which repr/__repr__ were originally invented for.
If repr is not that informative there will be some point in time, where
this information would be needed, and one (probably me) will have to
write say debug/__debug__, but why can't we have this sort of output
right from repr? What are cons of this? My point is that there is
str(expr) and also we can always use sympy.interactive and ipython.
--
Всего хорошего, Кирилл.
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