Example of Bpy with a plane object

b.py

data = bpy.data.objects['Plane'].data
data.vertices.add(1)
data.vertices[4].co.x=3

data.edges.add(2)
data.edges[4].vertices[0]=3
data.edges[4].vertices[1]=4
data.edges[5].vertices[0]=1
data.edges[5].vertices[1]=4

data.loops.add(3)
data.loops[4].vertex_index=1
data.loops[5].vertex_index=4
data.loops[6].vertex_index=3

data.polygons.add(1)
data.polygons[1].loop_start=4
data.polygons[1].loop_total=3