If there are no vars then you will supply them from free_symbols...and that
won't need to be sympified. It's a parallel structure to what you had above.


On Sun, Nov 10, 2013 at 12:56 PM, Sergey B Kirpichev <
notifications@github.com> wrote:

> In sympy/calculus/euler.py:
>
> > +        set([-Derivative(u(t, x), t, t) + Derivative(u(t, x), x, x) == 0])
> > +    """
> > +
> > +    if not isinstance(funcs, (tuple, list)):
> > +        funcs = (funcs,)
> > +    if not funcs:
> > +        funcs = tuple(L.atoms(Function))
> > +    for f in funcs:
> > +        if not isinstance(f, Function):
> > +            raise TypeError('Function expected, got: %r' % f)
> > +
> > +    if not isinstance(vars, (tuple, list)):
> > +        vars = (vars,)
> > +    if not vars:
> > +        vars = tuple(funcs[0].free_symbols)
> > +    vars = [sympify(var) for var in vars]
>
> But what's wrong with this?
>
> —
> Reply to this email directly or view it on GitHub<https://github.com/sympy/sympy/pull/2431/files#r7549630>
> .
>