On Dec 28, 2007 11:48 AM, Pearu Peterson <[EMAIL PROTECTED]> wrote:
>
>
>
> On Dec 28, 10:12 am, "Ondrej Certik" <[EMAIL PROTECTED]> wrote:
> > On Dec 28, 2007 10:18 AM, Pearu Peterson <[EMAIL PROTECTED]> wrote:
> >
>
> >
> > > Try deriving Foo from sympy.Basic. Actually the __mul__ code in sympy
> > > is broken as it should return NotImplemented when it gets an
> > > unknown (to sympy) object as an right hand side.
> >
> > It raises:
> >
> > Traceback (most recent call last):
> > File "t.py", line 21, in ?
> > y*f # does not work
> > File "/home/ondra/sympy/sympy/core/methods.py", line 32, in __mul__
> > return Basic.Mul(self, other)
> > File "sympy/core/basic_methods.py", line 122, in wrapper
> > func_cache_it_cache[k] = r = func(*args, **kw_args)
> > File "/home/ondra/sympy/sympy/core/operations.py", line 19, in __new__
> > c_part, nc_part, lambda_args, order_symbols =
> > cls.flatten(map(Basic.sympify, args))
> > File "sympy/core/basic.py", line 270, in sympify
> > raise ValueError("%r is NOT a valid SymPy expression" % a)
> > ValueError: '<__main__.Foo instance at 0xb7dbf14c>' is NOT a valid
> > SymPy expression
> >
> > So maybe we could check in the mul, if a ValueError exception gets
> > raised in sympify and reraise NotImplemented instead?
>
> sympify(obj) should try obj.__sympy__() if obj is unknown to sympy.
> If that fails then sympify should raise TypeError.
>
> For __mul__ method the sympify should take an optional argument,
> say `return_on_unsuccess=NotImplemented`, and return NotImplemented.
Right.
> Note that returning NotImplemented is not raising
> NotImplementedError.
You mean like
return NotImplemented
?
Wow, I didn't know about this:
>>> def f():
... return NotImplemented
...
>>> f()
NotImplemented
>>> type(f())
<type 'NotImplementedType'>
I learn something new everyday. :)
Ondrej
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