title: python search and write to file
body: <p>In the below code i am trying to replace the contents of a file which has the following content in it.
  <code>hellohello world</code> and the string hellohello should be replaced by hello and be wrote back to the file.Ho to go about this</p>
  
  <pre><code>  #!/usr/bin/python
    import os
  
    new_file_list=[]
    all_files=os.listdir("/tmp")
    for ff in all_files:
       if ff.endswith(".txt"):
          new_file_list.append(ff)
  
    for files in new_file_list:
       if files == "a.txt":
         print "======================================="
         file_name="/tmp/"+str(files)
         print file_name
         f=open(file_name ,"rw")
         while True:
           print "======================================="
           for line in f.readline():
              print line
              print "======================================="
              f.write(line.replace("hellohello","hello"))
              print line
           else:
              break
         for line in f.readline():
           print line
  
    f.close()
  </code></pre>