def Tail(filename, n_lines):
  """Return the last several lines of a file.

  If the file does not exist, an empty string is returned.

  Args:
    filename: Name of the file to read.
    n_lines: Number of lines to return.

  Returns:
    String containing the file data.
  """
  lines = []
  try:
    with open(filename, 'r') as f:
      lines = f.readlines()
  except IOError:
    pass
  return ''.join(lines[-n_lines:])