All,
On Sat, Jun 28, 2008 at 12:49:44PM +0200, Ondrej Certik wrote:
> Sorry for top posting, writing from a cell phone. I think we need to
> implement all printing ways we mentioned in this thread, probably in
> the Printer class just like pretty printing or latex. Then we will
> just call one in Basic.__str__ and another in Basic.__repr__ and
> remove all other str and repr methods. We can of course discuss which
> one to call from where, but then we'll be just discussing a change of
> exactly one line of code. As to other things, I agree with Fredrik.
> Fredrik, will you come to euroscipy or scipy2008, so that we can fix
> this together? It be awesome. :) All students here, please apply for
> sponsorship to scipy2008, so that enthought has some good students to
> choose from and that we can hack on sympy at Caltech.:) Ondrej
>
> On 6/27/08, Kirill Smelkov <[EMAIL PROTECTED]> wrote:
> >
> > 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.
Ok, after a bit of thinking, and good idea from Fredrik about
"appropriate context" in repr description, here is what I propose:
pprint(expr) -- nice looking 2D pretty-printed formula
str(expr) -- if possible nice loocking 1D formula, and
sympify(str(expr)) == expr invariant holds
repr(expr) -- internal representation of expr with class names and
other details, and
eval(repr(expr)) == expr invariant holds
Sounds reasonable?
--
Всего хорошего, Кирилл.
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