docs: def is_file_encrypted(self, filename):
          '''
          Given a file. Check if it is already encrypted.
          '''
          if not os.path.exists(filename):
              print "Invalid filename %s. Does not exist" % filename
              return False
  
          fhandle = open(filename, "rb")
          data = fhandle.read()
          fhandle.close()
  
          if data.startswith(AnsiVault.HEADER):
              return True
          else:
              return False