Expression.is_callable: New

src/sage/symbolic/expression.pyx

@@ -3124,6 +3124,22 @@ cdef class Expression(Expression_abc):
 
         return obj.is_square()
 
+    def is_callable(self):
+        r"""
+        Return ``True`` if ``self`` is a callable symbolic expression.
+
+        EXAMPLES::
+
+            sage: var('a x y z')
+            (a, x, y, z)
+            sage: f(x, y) = a + 2*x + 3*y + z
+            sage: f.is_callable()
+            True
+            sage: (a+2*x).is_callable()
+            False
+        """
+        return isinstance(self.parent(), sage.rings.abc.CallableSymbolicExpressionRing)
+
     def left_hand_side(self):
         """
         If self is a relational expression, return the left hand side
@@ -4632,7 +4648,7 @@ cdef class Expression(Expression_abc):
                 symb = vars[0]
             elif len(vars) == 0:
                 return self._parent(0)
-            elif sage.symbolic.callable.is_CallableSymbolicExpression(self):
+            elif self.is_callable():
                 return self.gradient()
             else:
                 raise ValueError("No differentiation variable specified.")
@@ -12714,7 +12730,6 @@ cdef class Expression(Expression_abc):
             sage: plot(f,0,1)
             Graphics object consisting of 1 graphics primitive
         """
-        from sage.symbolic.callable import is_CallableSymbolicExpression
         from sage.symbolic.ring import is_SymbolicVariable
         from sage.plot.plot import plot
 
@@ -12730,7 +12745,7 @@ cdef class Expression(Expression_abc):
                     break
 
         if param is None:
-            if is_CallableSymbolicExpression(self):
+            if self.is_callable():
                 A = self.arguments()
                 if len(A) == 0:
                     raise ValueError("function has no input arguments")