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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docstr: Create a new ``ShiftReduceParser``, that uses ``grammar`` to
  parse texts.
  
  :type grammar: Grammar
  :param grammar: The grammar used to parse texts.
  :type trace: int
  :param trace: The level of tracing that should be used when
      parsing a text.  ``0`` will generate no tracing output;
      and higher numbers will produce more verbose tracing
      output.
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code: def __init__(self, grammar, trace=0):
      """
      Create a new ``ShiftReduceParser``, that uses ``grammar`` to
      parse texts.
  
      :type grammar: Grammar
      :param grammar: The grammar used to parse texts.
      :type trace: int
      :param trace: The level of tracing that should be used when
          parsing a text.  ``0`` will generate no tracing output;
          and higher numbers will produce more verbose tracing
          output.
      """
      self._grammar = grammar
      self._trace = trace
      self._check_grammar()
  
imports: from nltk.grammar import Nonterminal
  from nltk.parse.api import ParserI
  from nltk.tree import Tree
label_desc: Use image node_id 1 to create a new ShiftReduceParser object from inherited base classes: ParserI with example: obj = ShiftReduceParser(grammar, trace)