Package nltk :: Package parse :: Module chart :: Class SteppingChartParser

Class SteppingChartParser

 object --+        
          |        
api.ParserI --+    
              |    
    ChartParser --+
                  |
                 SteppingChartParser

Known Subclasses:

SteppingChartParse

A ChartParser that allows you to step through the parsing process, adding a single edge at a time. It also allows you to change the parser's strategy or grammar midway through parsing a text.

The initialize method is used to start parsing a text. step adds a single edge to the chart. set_strategy changes the strategy used by the chart parser. parses returns the set of parses that has been found by the chart parser.

Instance Methods

[hide private]

__init__(self, grammar, strategy=None, trace=0)
Create a new chart parser, that uses grammar to parse texts. source code

initialize(self, tokens)
Begin parsing the given tokens.

source code

step(self)
Returns: A generator that adds edges to the chart, one at a time.

source code

_parse(self)
A generator that implements the actual parsing algorithm.

source code

strategy(self)
Returns: The strategy used by this parser.

source code

grammar(self)
Returns: The grammar used by this parser.

source code

chart(self)
Returns: The chart that is used by this parser.

source code

current_chartrule(self)
Returns: The chart rule used to generate the most recent edge.

source code

parses(self, tree_class=<class 'nltk.tree.Tree'>)
Returns: The parse trees currently contained in the chart.

source code

set_strategy(self, strategy)
Change the startegy that the parser uses to decide which edges to add to the chart.

source code

set_grammar(self, grammar)
Change the grammar used by the parser.

source code

set_chart(self, chart)
Load a given chart into the chart parser.

source code

list of Tree

nbest_parse(self, tokens, n=None, tree_class=<class 'nltk.tree.Tree'>)
Returns: A list of parse trees that represent possible structures for the given sentence.

source code

Inherited from api.ParserI: batch_iter_parse, batch_nbest_parse, batch_parse, batch_prob_parse, iter_parse, parse, prob_parse

Inherited from object: __delattr__, __getattribute__, __hash__, __new__, __reduce__, __reduce_ex__, __repr__, __setattr__, __str__

Deprecated

Inherited from api.ParserI: batch_test, get_parse, get_parse_dict, get_parse_list, get_parse_prob

Instance Variables

[hide private]

_restart
Records whether the parser's strategy, grammar, or chart has been changed.

Properties

[hide private]

Inherited from object: __class__

Method Details

[hide private]

init(self, grammar, strategy=None, trace=0)
(Constructor)

source code

Create a new chart parser, that uses grammar to parse texts.

Parameters:

grammar - The grammar used to parse texts.
strategy - A list of rules that should be used to decide what edges to add to the chart (top-down strategy by default).
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.

Overrides: ChartParser.__init__

(inherited documentation)

step(self)

source code

Returns:

A generator that adds edges to the chart, one at a time. Each time the generator is resumed, it adds a single edge and yields that edge. If no more edges can be added, then it yields None.

If the parser's strategy, grammar, or chart is changed, then the generator will continue adding edges using the new strategy, grammar, or chart.

Note that this generator never terminates, since the grammar or strategy might be changed to values that would add new edges. Instead, it yields None when no more edges can be added with the current strategy and grammar.

_parse(self)

source code

A generator that implements the actual parsing algorithm. step iterates through this generator, and restarts it whenever the parser's strategy, grammar, or chart is modified.

strategy(self)

source code

Returns:: The strategy used by this parser.

grammar(self)

source code

Returns:: The grammar used by this parser.
Overrides: ChartParser.grammar

chart(self)

source code

Returns:: The chart that is used by this parser.

current_chartrule(self)

source code

Returns:: The chart rule used to generate the most recent edge.

parses(self, tree_class=<class 'nltk.tree.Tree'>)

source code

Returns:: The parse trees currently contained in the chart.

set_strategy(self, strategy)

source code

Change the startegy that the parser uses to decide which edges to add to the chart.

Parameters:

strategy (list of ChartRuleI) - A list of rules that should be used to decide what edges to add to the chart.

nbest_parse(self, tokens, n=None, tree_class=<class 'nltk.tree.Tree'>)

source code

Parameters:

sent - The sentence to be parsed
n - The maximum number of trees to return.

Returns: list of Tree

A list of parse trees that represent possible structures for the given sentence. When possible, this list is sorted from most likely to least likely. If n is specified, then the returned list will contain at most n parse trees.

Overrides: ChartParser.nbest_parse

Instance Variable Details

[hide private]

_restart

Records whether the parser's strategy, grammar, or chart has been changed. If so, then step must restart the parsing algorithm.

Class SteppingChartParser

__init__(self, grammar, strategy=None, trace=0) (Constructor)

step(self)

_parse(self)

strategy(self)

grammar(self)

chart(self)

current_chartrule(self)

parses(self, tree_class=<class 'nltk.tree.Tree'>)

set_strategy(self, strategy)

nbest_parse(self, tokens, n=None, tree_class=<class 'nltk.tree.Tree'>)

_restart

init(self, grammar, strategy=None, trace=0)
(Constructor)