code: def format_int(n, singular=_Default, plural=_Default):
      
      n = int(n)
  
      if singular in (None, _Default):
          if plural is _Default:
              plural = None
  
          singular = u'{:,}'
  
      elif plural is _Default:
          plural = singular + u's'
  
      if n == 1 or not plural:
          return singular.format(n)
  
      return plural.format(n)
docs: Return `singular.format(n)` if n is 1, or `plural.format(n)` otherwise. If
      plural is not specified, then it is assumed to be same as singular but
      suffixed with an 's'.
  
      :param n:
          Integer which determines pluralness.
  
      :param singular:
          String with a format() placeholder for n. (Default: `u"{:,}"`)
  
      :param plural:
          String with a format() placeholder for n. (Default: If singular is not
          default, then it's `singular + u"s"`. Otherwise it's same as singular.)
  
      Example: ::
  
          >>> r(format_int(1000))
          u'1,000'
          >>> r(format_int(1, u"{} day"))
          u'1 day'
          >>> r(format_int(2, u"{} day"))
          u'2 days'
          >>> r(format_int(2, u"{} box", u"{} boxen"))
          u'2 boxen'
          >>> r(format_int(20000, u"{:,} box", u"{:,} boxen"))
          u'20,000 boxen'