sel_objs = [obj for obj in bpy.context.selected_objects]
for obj in sel_objs:
    obj.select = True
    ob = bpy.context.active_object
    action = ob.animation_data.action
    keyframes = []
    for fcu in action.fcurves:
        for kp in fcu.keyframe_points:
            if kp.co[0] not in keyframes:
                keyframes.append(kp.co[0])
    with open('blender_data.txt' , 'w') as f:
        for i in range(len(keyframes)):
            k = keyframes[i]
            bpy.context.scene.frame_set(k)
            f.write(ob.name + ', ')
            f.write(str(float(ob.location.x)) + ', ' + str(float(ob.location.y)) + ', ' + str(float(ob.location.z)) + ', ')
            f.write(str(float(ob.scale.x)) + ', ' + str(float(ob.scale.y)) + ', ' + str(float(ob.scale.z)) + ', ')
            f.write('%s n' % (k))
    obj.select = False

Traceback (most recent call last):
  File "<blender_console>", line 4, in <module>
AttributeError: 'NoneType' object has no attribute 'action'