nltk.grammar.FeatureGrammar

class documentation

class FeatureGrammar(CFG): (source)

Constructor: FeatureGrammar(start, productions)

A feature-based grammar. This is equivalent to a CFG whose nonterminals are all FeatStructNonterminal.

A grammar consists of a start state and a set of productions. The set of terminals and nonterminals is implicitly specified by the productions.

Class Method	`fromstring`	Return a feature structure based grammar.
Method	`__init__`	Create a new feature-based grammar, from the given start state and set of `Productions`.
Method	`leftcorner_parents`	Return the set of all categories for which the given category is a left corner.
Method	`leftcorners`	Return the set of all words that the given category can start with. Also called the "first set" in compiler construction.
Method	`productions`	Return the grammar productions, filtered by the left-hand side or the first item in the right-hand side.
Method	`_calculate_indexes`	Undocumented
Method	`_get_type_if_possible`	Helper function which returns the `TYPE` feature of the `item`, if it exists, otherwise it returns the `item` itself
Instance Variable	`_empty_index`	Undocumented
Instance Variable	`_empty_productions`	Undocumented
Instance Variable	`_lexical_index`	Undocumented
Instance Variable	`_lhs_index`	Undocumented
Instance Variable	`_rhs_index`	Undocumented

Inherited from CFG:

Class Method	`binarize`	Convert all non-binary rules into binary by introducing new tokens. Example:: Original:
Class Method	`eliminate_start`	Eliminate start rule in case it appears on RHS Example: S -> S0 S1 and S0 -> S1 S Then another rule S0_Sigma -> S is added
Class Method	`remove_unitary_rules`	Remove nonlexical unitary rules and convert them to lexical
Method	`__repr__`	Undocumented
Method	`__str__`	Undocumented
Method	`check_coverage`	Check whether the grammar rules cover the given list of tokens. If not, then raise an exception.
Method	`chomsky_normal_form`	Returns a new Grammer that is in chomsky normal :param: new_token_padding
Method	`is_binarised`	Return True if all productions are at most binary. Note that there can still be empty and unary productions.
Method	`is_chomsky_normal_form`	Return True if the grammar is of Chomsky Normal Form, i.e. all productions are of the form A -> B C, or A -> "s".
Method	`is_flexible_chomsky_normal_form`	Return True if all productions are of the forms A -> B C, A -> B, or A -> "s".
Method	`is_leftcorner`	True if left is a leftcorner of cat, where left can be a terminal or a nonterminal.
Method	`is_lexical`	Return True if all productions are lexicalised.
Method	`is_nonempty`	Return True if there are no empty productions.
Method	`is_nonlexical`	Return True if all lexical rules are "preterminals", that is, unary rules which can be separated in a preprocessing step.
Method	`max_len`	Return the right-hand side length of the longest grammar production.
Method	`min_len`	Return the right-hand side length of the shortest grammar production.
Method	`start`	Return the start symbol of the grammar
Method	`_calculate_grammar_forms`	Pre-calculate of which form(s) the grammar is.
Method	`_calculate_leftcorners`	Undocumented
Instance Variable	`_all_unary_are_lexical`	Undocumented
Instance Variable	`_categories`	Undocumented
Instance Variable	`_immediate_leftcorner_categories`	Undocumented
Instance Variable	`_immediate_leftcorner_words`	Undocumented
Instance Variable	`_is_lexical`	Undocumented
Instance Variable	`_is_nonlexical`	Undocumented
Instance Variable	`_leftcorner_parents`	Undocumented
Instance Variable	`_leftcorner_words`	Undocumented
Instance Variable	`_leftcorners`	Undocumented
Instance Variable	`_max_len`	Undocumented
Instance Variable	`_min_len`	Undocumented
Instance Variable	`_productions`	Undocumented
Instance Variable	`_start`	Undocumented

@classmethod
def fromstring(cls, input, features=None, logic_parser=None, fstruct_reader=None, encoding=None): (source) ¶

overrides nltk.grammar.CFG.fromstring

Return a feature structure based grammar.

as a list of strings. :param features: a tuple of features (default: SLASH, TYPE) :param logic_parser: a parser for lambda-expressions, by default, LogicParser() :param fstruct_reader: a feature structure parser (only if features and logic_parser is None)

Parameters
input	a grammar, either in the form of a string or else
features	Undocumented
logic_parser	Undocumented
fstruct_reader	Undocumented
encoding	Undocumented

def __init__(self, start, productions): (source) ¶

overrides nltk.grammar.CFG.__init__

Create a new feature-based grammar, from the given start state and set of Productions.

Parameters
start:FeatStructNonterminal	The start symbol
productions:list(Production)	The list of productions that defines the grammar

def leftcorner_parents(self, cat): (source) ¶

overrides nltk.grammar.CFG.leftcorner_parents

Return the set of all categories for which the given category is a left corner.

def leftcorners(self, cat): (source) ¶

overrides nltk.grammar.CFG.leftcorners

Return the set of all words that the given category can start with. Also called the "first set" in compiler construction.

def productions(self, lhs=None, rhs=None, empty=False): (source) ¶

overrides nltk.grammar.CFG.productions

Return the grammar productions, filtered by the left-hand side or the first item in the right-hand side.

Parameters
lhs	Only return productions with the given left-hand side.
rhs	Only return productions with the given first item in the right-hand side.
empty	Only return productions with an empty right-hand side.
Returns
list(Production)	Undocumented