How to flip a normal of a selected face?

I want to flip a normal of a selected face.
But, except using a bpy.ops.mesh.flip_normals().

Perhaps, is there a otherwise way.

Please answer to me.
Thank you.

It’s straight-forward with bmesh module:

bm = bmesh.from_edit_mesh(me)
bm.faces[0].normal_flip()

Standard API doesn’t seem to offer a low-level way.

Thank you.
This problem was solved with your reply.