old_contents: #!/usr/bin/env python
  #
  # Prepend each line in a file with a fixed string.
  #
  
  import fileinput
  import sys
  
  for playlist in sys.argv[1:]:
      for line in fileinput.input([playlist], inplace=True):
          sys.stdout.write('../music/{l}'.format(l=line))
  
new_contents: #!/usr/bin/env python
  #
  # Prepend each line in a file with a fixed string.
  #
  
  import fileinput
  import sys
  
  for playlist in sys.argv[1:]:
      for line in fileinput.input([playlist], inplace=True):
          sys.stdout.write('/<microSD1>/music/{l}'.format(l=line))
  
subject: prepend an absolute partial path instead of a relative one