Trac #17311: polynomial_real_mpfr_dense.call() accepts only 1 arg

burcin mentions in comment 2 of #9769:

The `__call__()` function of RR[x] doesn't conform to the generic
definition. You should be able to give the parameters as a keyword
argument as well. This should be made to work:

{{{
sage: R.<x> = RR[]
sage: (x^2+1)(x=5)
26.0000000000000
}}}

URL: http://trac.sagemath.org/17311
Reported by: rws
Ticket author(s): Ralf Stephan
Reviewer(s): Marc Mezzarobba

src/sage/rings/polynomial/polynomial_real_mpfr_dense.pyx

@@ -641,7 +641,7 @@ cdef class PolynomialRealDense(Polynomial):
         else:
             return a * ~a[a.degree()] << min(aval, bval)
 
-    def __call__(self, xx):
+    def __call__(self, *args, **kwds):
         """
         EXAMPLES::
 
@@ -669,16 +669,29 @@ cdef class PolynomialRealDense(Polynomial):
             sage: f = PolynomialRealDense(RR['x'])
             sage: f(12)
             0.000000000000000
+            
+        TESTS::
+        
+            sage: R.<x> = RR[]       # :trac:`17311`
+            sage: (x^2+1)(x=5)
+            26.0000000000000
         """
+        if len(args) == 1:
+            xx = args[0]
+        else:
+            return Polynomial.__call__(self, *args, **kwds)
+
         if not PY_TYPE_CHECK(xx, RealNumber):
             if self._base_ring.has_coerce_map_from(parent(xx)):
                 xx = self._base_ring(xx)
             else:
                 return Polynomial.__call__(self, xx)
+
         cdef Py_ssize_t i
         cdef mp_rnd_t rnd = self._base_ring.rnd
         cdef RealNumber x = <RealNumber>xx
         cdef RealNumber res
+
         if (<RealField_class>x._parent).__prec < self._base_ring.__prec:
             res = RealNumber(x._parent)
         else:
@@ -704,7 +717,7 @@ cdef class PolynomialRealDense(Polynomial):
                 mpfr_mul(res.value, res.value, x.value, rnd)
                 mpfr_add(res.value, res.value, self._coeffs[i], rnd)
         return res
-
+    
     def change_ring(self, R):
         """
         EXAMPLES::