class_docstr: A simple bottom-up CFG parser that uses two operations, "shift"
  and "reduce", to find a single parse for a text.
  
  ``ShiftReduceParser`` maintains a stack, which records the
  structure of a portion of the text.  This stack is a list of
  strings and Trees that collectively cover a portion of
  the text.  For example, while parsing the sentence "the dog saw
  the man" with a typical grammar, ``ShiftReduceParser`` will produce
  the following stack, which covers "the dog saw"::
  
     [(NP: (Det: 'the') (N: 'dog')), (V: 'saw')]
  
  ``ShiftReduceParser`` attempts to extend the stack to cover the
  entire text, and to combine the stack elements into a single tree,
  producing a complete parse for the sentence.
  
  Initially, the stack is empty.  It is extended to cover the text,
  from left to right, by repeatedly applying two operations:
  
    - "shift" moves a token from the beginning of the text to the
      end of the stack.
    - "reduce" uses a CFG production to combine the rightmost stack
      elements into a single Tree.
  
  Often, more than one operation can be performed on a given stack.
  In this case, ``ShiftReduceParser`` uses the following heuristics
  to decide which operation to perform:
  
    - Only shift if no reductions are available.
    - If multiple reductions are available, then apply the reduction
      whose CFG production is listed earliest in the grammar.
  
  Note that these heuristics are not guaranteed to choose an
  operation that leads to a parse of the text.  Also, if multiple
  parses exists, ``ShiftReduceParser`` will return at most one of
  them.
  
  :see: ``nltk.grammar``
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code: def grammar(self):
      return self._grammar
  
imports: from nltk.grammar import Nonterminal
  from nltk.parse.api import ParserI
  from nltk.tree import Tree
label_desc: Use image node_id 2 for calling the ShiftReduceParser obj's underlying member method code with example usage: obj.grammar() and returns: self