On Tue, Dec 10, 2013 at 01:22:33PM -0800, Christopher Smith wrote:
>    In sympy/core/tests/test_match.py:
> 
>  > @@ -216,7 +216,7 @@ def test_derivative1():
>  >      x, y = map(Symbol, 'xy')
>  >      p, q = map(Wild, 'pq')
>  >
>  > -    f = Function('f', nargs=1)
> 
>    because it doesn't work; I agree that it's a good idea and this is the
>    thing that I asked if you could undertake: make a setter so this *does*
>    work and then we can get rid of the bad idea of touching `_nargs`

First, it was working before.  It's just a constructor, no
needs for a setter method.

Second, it's not about touching _nargs.  But if we adopt this (or if
we implement a setter method) - Function instance will be not immutable.