#18036 minor code adaptations in rings/

src/sage/rings/complex_mpc.pyx

@@ -863,14 +863,9 @@ cdef class MPComplexNumber(sage.structure.element.FieldElement):
                 real, imag = z
             elif isinstance(z, complex):
                 real, imag = z.real, z.imag
-            elif isinstance(z, sage.symbolic.expression.Expression):
-                zz = sage.rings.complex_mpfr.ComplexField(self._parent.prec())(z)
-                self._set(zz)
-                return
             elif type(z) is gmpy2.mpc:
                 mpc_set(self.value, (<gmpy2.mpc>z).c, rnd)
                 return
-            # then, no imaginary part
             elif type(z) is gmpy2.mpfr:
                 mpc_set_fr(self.value, (<gmpy2.mpfr>z).f, rnd)
                 return
@@ -891,8 +886,13 @@ cdef class MPComplexNumber(sage.structure.element.FieldElement):
                 mpc_set_si(self.value, z, rnd)
                 return
             else:
-                real = z
-                imag = 0
+                C = sage.rings.complex_mpfr.ComplexField(self._parent.prec())
+                if C.has_coerce_map_from(z.parent()) or isinstance(z, sage.symbolic.expression.Expression):
+                    self._set(C(z))
+                    return
+                else:
+                    real = z
+                    imag = 0
         else:
             real = z
             imag = y

src/sage/rings/polynomial/polynomial_rational_flint.pyx

@@ -667,7 +667,7 @@ cdef class Polynomial_rational_flint(Polynomial):
         else:
             try:
                 len = <unsigned long> (degree + 1)
-            except ValueError:
+            except (TypeError, ValueError):
                 raise ValueError('degree must be convertible to long')
 
         res = self._new()