How I can check if the selected vertices already form a face?

I Tried to avoid the next:
http://s3.subirimagenes.com:81/otros/previo/thump_7174750face.jpg

I know that with this line of code, I can create the face: “bpy.ops.mesh.edge_face_add()”
But I don´t know, with which command I can identified that I have a face created, to avoid the warning in the System Console, how I can check that?
Thanks for the help ¡¡.