import os 
import os.path as osp

rootdir = "C:\YSRVOC\VOCdevkit\VOC2007\JPEGImages"
file_object = open('C:\YSRVOC\VOCdevkit\VOC2007\ImageSets\Main/train.txt','w')
for parent,dirnames,filenames in os.walk(rootdir):
    for filename in filenames:
        filename=filename.partition(".")
        print (filename)
        file_object.write(filename[0]+ '\n')
file_object.close()