nltk.parse

Package parse

Classes and interfaces for producing tree structures that represent the internal organization of a text. This task is known as parsing the text, and the resulting tree structures are called the text's parses. Typically, the text is a single sentence, and the tree structure represents the syntactic structure of the sentence. However, parsers can also be used in other domains. For example, parsers can be used to derive the morphological structure of the morphemes that make up a word, or to derive the discourse structure for a set of utterances.

Sometimes, a single piece of text can be represented by more than one tree structure. Texts represented by more than one tree structure are called ambiguous texts. Note that there are actually two ways in which a text can be ambiguous:

The text has multiple correct parses.

There is not enough information to decide which of several candidate parses is correct.

However, the parser module does not distinguish these two types of ambiguity.

The parser module defines ParserI, a standard interface for parsing texts; and two simple implementations of that interface, ShiftReduceParser and RecursiveDescentParser. It also contains three sub-modules for specialized kinds of parsing:

nltk.parser.chart defines chart parsing, which uses dynamic programming to efficiently parse texts.

nltk.parser.probabilistic defines probabilistic parsing, which associates a probability with each parse.

Submodules

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nltk.parse.api
nltk.parse.chart: Data classes and parser implementations for "chart parsers", which use dynamic programming to efficiently parse a text.
nltk.parse.dependencygraph: Tools for reading and writing dependency trees.
nltk.parse.earleychart: Data classes and parser implementations for incremental chart parsers, which use dynamic programming to efficiently parse a text.
nltk.parse.featurechart: Extension of chart parsing implementation to handle grammars with feature structures as nodes.
nltk.parse.generate
nltk.parse.malt
nltk.parse.nonprojectivedependencyparser
nltk.parse.pchart: Classes and interfaces for associating probabilities with tree structures that represent the internal organization of a text.
nltk.parse.projectivedependencyparser
nltk.parse.rd
nltk.parse.sr
nltk.parse.util: Utility functions for parsers.
nltk.parse.viterbi

Classes

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FeatureIncrementalBottomUpLeftCornerChartParser

LeftCornerChartParser

IncrementalTopDownChartParser

FeatureIncrementalBottomUpChartParser

FeatureEarleyChartParser

FeatureBottomUpChartParser

EarleyChartParser

IncrementalBottomUpChartParser

FeatureTopDownChartParser

BottomUpChartParser
A ChartParser using a bottom-up parsing strategy.

IncrementalLeftCornerChartParser

TopDownChartParser
A ChartParser using a top-down parsing strategy.

IncrementalBottomUpLeftCornerChartParser

BottomUpLeftCornerChartParser
A ChartParser using a bottom-up left-corner parsing strategy.

FeatureBottomUpLeftCornerChartParser

FeatureIncrementalChartParser

SteppingChartParser
A ChartParser that allows you to step through the parsing process, adding a single edge at a time.

FeatureIncrementalTopDownChartParser

IncrementalChartParser
An incremental chart parser implementing Jay Earley's parsing algorithm:

LongestChartParser
A bottom-up parser for PCFGs that tries longer edges before shorter ones.

UnsortedChartParser
A bottom-up parser for PCFGs that tries edges in whatever order.

BottomUpProbabilisticChartParser
An abstract bottom-up parser for PCFGs that uses a Chart to record partial results.

RandomChartParser
A bottom-up parser for PCFGs that tries edges in random order.

SteppingRecursiveDescentParser
A RecursiveDescentParser that allows you to step through the parsing process, performing a single operation at a time.

RecursiveDescentParser
A simple top-down CFG parser that parses texts by recursively expanding the fringe of a Tree, and matching it against a text.

SteppingShiftReduceParser
A ShiftReduceParser that allows you to setp through the parsing process, performing a single operation at a time.

ShiftReduceParser
A simple bottom-up CFG parser that uses two operations, "shift" and "reduce", to find a single parse for a text.

FeatureChartParser

InsideChartParser
A bottom-up parser for PCFGs that tries edges in descending order of the inside probabilities of their trees.

ChartParser
A generic chart parser.

ViterbiParser
A bottom-up PCFG parser that uses dynamic programming to find the single most likely parse for a text.

ProbabilisticProjectiveDependencyParser
A probabilistic, projective dependency parser.

ProjectiveDependencyParser
A projective, rule-based, dependency parser.

NaiveBayesDependencyScorer
A dependency scorer built around a MaxEnt classifier.

ProbabilisticNonprojectiveParser
A probabilistic non-projective dependency parser.

NonprojectiveDependencyParser
A non-projective, rule-based, dependency parser.

ParserI
A processing class for deriving trees that represent possible structures for a sequence of tokens.

DependencyGraph
A container for the nodes and labelled edges of a dependency structure.

MaltParser

Functions

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load_parser(grammar_url, trace=0, parser=None, chart_class=None, beam_size=0, **load_args)
Load a grammar from a file, and build a parser based on that grammar.

source code

XDigraph

nx_graph(self)
Convert the data in a nodelist into a networkx labeled directed graph. source code

Function Details

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load_parser(grammar_url, trace=0, parser=None, chart_class=None, beam_size=0, **load_args)

source code

Load a grammar from a file, and build a parser based on that grammar. The parser depends on the grammar format, and might also depend on properties of the grammar itself.

The following grammar formats are currently supported:

'cfg' (CFGs: ContextFreeGrammar)
'pcfg' (probabilistic CFGs: WeightedGrammar)
'fcfg' (feature-based CFGs: ContextFreeGrammar)

Parameters:

grammar_url (str) - A URL specifying where the grammar is located. The default protocol is "nltk:", which searches for the file in the the NLTK data package.
trace (int) - 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.
parser - The class used for parsing; should be ChartParser or a subclass. If None, the class depends on the grammar format.
chart_class - The class used for storing the chart; should be Chart or a subclass. Only used for CFGs and feature CFGs. If None, the chart class depends on the grammar format.
beam_size (int) - The maximum length for the parser's edge queue. Only used for probabilistic CFGs.
load_args - Keyword parameters used when loading the grammar. See data.load for more information.