def file_handler1():
     file1=open("test1.txt","a")
     file2=open("test2.txt","r")
     file3=open("new.txt", "w")
     file3.write(file2.read())

 def file_handler2():
     CMD="cat test1.txt test2.txt > new.txt"
     S.call([CMD],shell=True)

 for i in range(1000):
     file_handler1()