How to insert some words in the txt file
<p>Now I want to add some words in a file, but I could only add some words in the end of file(.txt) via using f.open('xxx.txt','a')
If I use 'a+' mode, the words will take place the old one from beginning. I hope to insert some sentences in the first line without change the original ones.  </p>

<pre><code># using python 2.7.12
  f = open('Bob.txt','w')
  f.write('How many roads must a man walk down'

  ' \nBefore they call him a man'

  ' \nHow many seas must a white dove sail'

  ' \nBefore she sleeps in the sand'

  ' \nHow many times must the cannon balls fly'

  " \nBefore they're forever banned"

  " \nThe answer my friend is blowing in the wind"

  " \nThe answer is blowing in the wind")
  f.close()
  # add spice to the song
  f1 = open('Bob.txt','a')
  f1.write("\n1962 by Warner Bros.inc.")
  f1.close()
  # print song
  f2 = open('Bob.txt','r')
  a = f2.read()
  print a
</code></pre>

<p>I hope to insert " Bob Dylan" in the first line, What code shall I add ?</p>