Fix for change in printing for function_symbol.diff

Author: isuruf

symengine/lib/symengine_wrapper.pyx

@@ -742,7 +742,7 @@ cdef class Number(Basic):
 
     @property
     def is_nonpositive(self):
-        return not (self.is_complex or self.is_nonpositive)
+        return not (self.is_complex or self.is_positive)
 
     @property
     def is_complex(self):

symengine/tests/test_functions.py

@@ -80,7 +80,7 @@ def test_abs_diff():
 def test_Subs():
     x = Symbol("x")
     y = Symbol("y")
-    _x = Symbol("_x")
+    _x = Symbol("_xi_1")
     f = function_symbol("f", 2*x)
     assert f.diff(x) == 2 * Subs(Derivative(function_symbol("f", _x), [_x]), [_x], [2 * x])
     assert Subs(Derivative(function_symbol("f", x, y), [x]), [x, y], [_x, x]) \