text: import xml.etree.ElementTree as ET
  import pickle
  import os
  from os import listdir, getcwd
  from os.path import join
  
  sets=[ ('2007', 'train'), ('2007', 'val'), ('2007', 'test')]
  
  classes = ["aeroplane", "bicycle", "bird", "boat", "bottle", "bus", "car", "cat", "chair", "cow", "diningtable", "dog", "horse", "motorbike", "person", "pottedplant", "sheep", "sofa", "train", "tvmonitor"]
  
  
  def convert(size, box):
      dw = 1./size[0]
      dh = 1./size[1]
      x = (box[0] + box[1])/2.0
      y = (box[2] + box[3])/2.0
      w = box[1] - box[0]
      h = box[3] - box[2]
      x = x*dw
      w = w*dw
      y = y*dh
      h = h*dh
      return (x,y,w,h)
  
  def convert_annotation(year, image_id):
      in_file = open('VOCdevkit/VOC%s/Annotations/%s.xml'%(year, image_id))
      out_file = open('VOCdevkit/VOC%s/labels/%s.txt'%(year, image_id), 'w')
      tree=ET.parse(in_file)
      root = tree.getroot()
      size = root.find('size')
      w = int(size.find('width').text)
      h = int(size.find('height').text)
  
      for obj in root.iter('object'):
          difficult = obj.find('difficult').text
          cls = obj.find('name').text
          if cls not in classes or int(difficult) == 1:
              continue
          cls_id = classes.index(cls)
          xmlbox = obj.find('bndbox')
          b = (float(xmlbox.find('xmin').text), float(xmlbox.find('xmax').text), float(xmlbox.find('ymin').text), float(xmlbox.find('ymax').text))
          bb = convert((w,h), b)
          out_file.write(str(cls_id) + " " + " ".join([str(a) for a in bb]) + '\n')
  
  wd = getcwd()
  
  for year, image_set in sets:
      if not os.path.exists('VOCdevkit/VOC%s/labels/'%(year)):
          os.makedirs('VOCdevkit/VOC%s/labels/'%(year))
      image_ids = open('VOCdevkit/VOC%s/ImageSets/Main/%s.txt'%(year, image_set)).read().strip().split()
      list_file = open('%s_%s.txt'%(year, image_set), 'w')
      for image_id in image_ids:
          list_file.write('%s/VOCdevkit/VOC%s/JPEGImages/%s.jpg\n'%(wd, year, image_id))
          convert_annotation(year, image_id)
      list_file.close()
  
  