obj_exporter_v1.py

import bpy

obj = bpy.context.active_object
mesh = obj.data

filepath_out = "/home/zeffii/Desktop/temp/single_line.obj"
with open(filepath_out, 'w') as ofile:

    begin = "OBJ File: "
    ofile.write(begin)

    for v in mesh.vertices:
        line = "{0} {1} "
        v_sanitized = v.co.to_tuple(4)  # precision 4
        v_as_string = str(v_sanitized)[1:-1]
        line = line.format("v", v_as_string).replace(",", "")
        # print(line)
        ofile.write(line)

    for f in mesh.polygons:
        line = "{0} {1} "
        f_as_string = str(f.vertices[:])[1:-1]
        line = line.format("f", f_as_string).replace(",", "")
        # print(line)
        ofile.write(line)