NumberField._pushout_: If AA, QQbar cannot be imported, just return None

Author: Matthias Koeppe

src/sage/rings/number_field/number_field_base.pyx

@@ -135,13 +135,15 @@ cdef class NumberField(Field):
         else:
             codomain_other = other
 
-        from sage.rings.qqbar import AA
-        if codomain_self is AA and codomain_other is AA:
-            return AA
-
-        from sage.rings.qqbar import QQbar
-        if codomain_self in (AA, QQbar) and codomain_other in (AA, QQbar):
-            return QQbar
+        try:
+            from sage.rings.qqbar import AA, QQbar
+        except ImportError:
+            pass
+        else:
+            if codomain_self is AA and codomain_other is AA:
+                return AA
+            if codomain_self in (AA, QQbar) and codomain_other in (AA, QQbar):
+                return QQbar
 
     def ring_of_integers(self, *args, **kwds):
         r"""