The Inline Markup :const: shows up in the final documentation. Example
can be found on http://docs.python.org/library/select.html :

kevent.fflags¶

    Filter specific flags

    :const:`KQ_FILTER_READ` and :const:`KQ_FILTER_WRITE` filter flags
    Constant 	Meaning
    KQ_NOTE_LOWAT 	low water mark of a socket buffer

    :const:`KQ_FILTER_VNODE` filter flags

It also shows up in the equivalent PDF documentation. The underlying rst
file is library/select.rst, relevant part of source text follows:
   *:const:`KQ_FILTER_READ` and  :const:`KQ_FILTER_WRITE` filter flags*

  
+----------------------------+--------------------------------------------+
   | Constant                   | Meaning                              
     |
  
+============================+============================================+
   | :const:`KQ_NOTE_LOWAT`     | low water mark of a socket buffer    
     |
  
+----------------------------+--------------------------------------------+


   *:const:`KQ_FILTER_VNODE` filter flags*


There is one more occurrance of :const: in
http://docs.python.org/library/cookielib.html:
...
Cookie.is_expired([now=:const:`None`])¶
    True if cookie ...