def Commas(value):
    """Formats an integer with thousands-separating commas.

  Args:
    value: An integer.

  Returns:
    A string.
  """
    if value < 0:
        sign = '-'
        value = -value
    else:
        sign = ''
    result = []
    while value >= 1000:
        result.append('%03d' % (value % 1000))
        value /= 1000
    result.append('%d' % value)
    return sign + ','.join(reversed(result))
