Le mercredi 01 juin 2011 à 20:12 -0600, Aaron Meurer a écrit :
> A few things:
>
> - Even if we made isympy play nice, doctests assume just a regular
> pure Python shell. So any doctest of a function that somehow has a
> list, tuple, or dict of sympy objects would have to be changed to
> either use less nice format (srepr()), or to use a printer that gets
> around it.
>
Well, we're already running doctests under our own printer - that's why
we had to essentially fork doctest from the stdlib. I think bin/doctest
doesn't actually execute any __repr__() method from sympy objects.
> - If we fix issue 2359, then I'd say about 90% of "typical" SymPy
> expressions would work with eval(str(x)) == x, assuming that Symbols
> have been instantiated (both str and srepr require "from sympy import
> *"). And as we know, sympify(str(x)) == x should *always* work
> assuming the expression is "generic" enough (i.e., standard functions
> like sin() or exp() haven't been overridden, Symbols have default
> assumptions, etc.).
>
> srepr() also does things like Add(Symbol('x'), Symbol('y')) instead of
> Symbol('x') + Symbol('y'), which I guess is more efficient so should
> probably stay as long as srepr() is the *really* long form of an
> expression.
>
> - I use .args mainly to get at some part of an expression that I don't
> want to re-type. If this always return the srepr() expression, that
> would be useless. Granted, I always use isympy, which uses pprint,
> not str, but I just wanted to point out that .args is not just used
> for debugging.
>
> - But even considering debugging, the srepr() form is, in my opinion,
> less useful for SymPy expressions than str(). From what I gathered
> from the discussions I saw on this on the Python mailing list and
> elsewhere, SymPy is rather unique in the fact that str(expr) <
> srepr(expr) by quite a bit for all but trivial expressions.
> Pow(Add(Symbol('x'), Mul(Symbol('x'), Symbol('y')), Pow(Symbol('x'),
> Integer(2))), Rational(1, 2)) is only more useful than sqrt(x**2 + x*y
> + x) if you want the eval(repr(x)) == x, which (unfortunately) doesn't
> really apply in list/tuple/dict's calling of __repr__ with __str__.
>
OK, srepr(x**2 + x*y + x) is unreadable, but it could be improved by
indenting and falling back to a more condensed representation beyond a
certain depth in the expression tree. For instance:
Pow(
Add(Symbol('x'), Mul(x, y), Pow(x, 2)),
Rational(1, 2)
)
> Aaron Meurer
>
> On Sun, May 29, 2011 at 1:07 PM, Ronan Lamy <[email protected]> wrote:
> > Le dimanche 29 mai 2011 à 08:25 -0700, Vinzent Steinberg a écrit :
> >> On 28 Mai, 17:40, Ronan Lamy <[email protected]> wrote:
> >> > I don't care about that, because we don't put stuff inside containers
> >> > that often, because I usually want the repr when I look at .args, and
> >> > because the only shell I really care about is ipython, which prints this
> >> > nicely in any case.
> >>
> >> I care about pure python shells. However, I could live with it if
> >> there was a trivial way to setup printing as in isympy (calling
> >> init_printing() probably already does this).
> >>
> > There is:
> >
> > ronan@ronan-desktop:~/Projets/sympy-git$ python
> > Python 2.7.1+ (r271:86832, Apr 11 2011, 18:05:24)
> > [GCC 4.5.2] on linux2
> > Type "help", "copyright", "credits" or "license" for more information.
> >>>> from sympy import *
> >>>> import sys
> >>>> sys.displayhook = pprint
> >>>> class A(object):
> > ... def __str__(self): return "A"
> > ...
> >>>> A()
> > A
> >>>> [A()]
> > [A]
> >>>> str([A()])
> > [<__main__.A object at 0x9d2024c>]
> >
> >> > What matters is that:
> >> > * we can't change it
> >> > * people new to sympy who know Python expect it
> >> > * there is a lot of code outside sympy that takes this behaviour for
> >> > granted and works with/around it.
> >>
> >> On the other hand, eval(repr(x)) == x does not hold in general, see
> >> for example lambda, functions, numpy arrays etc.
> >
> > Sure. But what I meant by "this behaviour" is the fact that str() is
> > supposed to be the nice, human-friendly representation of the object,
> > while repr() shows what's actually inside the object, and that the str()
> > of built-in containers isn't actually nice enough for most uses.
> >
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