code: def enablePackrat():
          
          if not ParserElement._packratEnabled:
              ParserElement._packratEnabled = True
              ParserElement._parse = ParserElement._parseCache
docs: Enables "packrat" parsing, which adds memoizing to the parsing logic.
             Repeated parse attempts at the same string location (which happens
             often in many complex grammars) can immediately return a cached value,
             instead of re-executing parsing/validating code.  Memoizing is done of
             both valid results and parsing exceptions.
  
             This speedup may break existing programs that use parse actions that
             have side-effects.  For this reason, packrat parsing is disabled when
             you first import pyparsing.  To activate the packrat feature, your
             program must call the class method C{ParserElement.enablePackrat()}.  If
             your program uses C{psyco} to "compile as you go", you must call
             C{enablePackrat} before calling C{psyco.full()}.  If you do not do this,
             Python will crash.  For best results, call C{enablePackrat()} immediately
             after importing pyparsing.