An example of Python scripting using gease pencil scripting for Blender. A partial re-invention of the "Convert Grease Pencil" operator.

grease_pencil_scripting.py

def make_basic_curve():
    crv = bpy.data.curves.new("crv", type="CURVE")
    crv_ob = bpy.data.objects.new("crv_ob", crv)
    return crv, crv_ob


scnobs = bpy.context.scene.objects

pencil = bpy.data.grease_pencil[0]
for i, stroke in enumerate(pencil.layers[0].active_frame.strokes):
    crv, crv_ob = make_basic_curve()
    scnobs.link(crv_ob)
    
    stroke_points = pencil.layers[0].active_frame.strokes[i].points
    data_list = [ (point.co.x, point.co.y, point.co.z) 
                    for point in stroke_points ]
    points_to_add = len(data_list)-1
    
    flat_list = []
    for point in data_list:
        flat_list.extend(point)
    
    spline = crv.splines.new(type="BEZIER")
    spline.bezier_points.add(points_to_add)
    spline.bezier_points.foreach_set("co", flat_list)
    
    for point in spline.bezier_points:
        point.handle_left_type="AUTO"
        point.handle_right_type="AUTO"