Package nltk_lite :: Package parse :: Module category :: Class Category

Class Category

                       object --+    
                                |    
featurestructure.FeatureStructure --+
                                    |
                       object --+   |
                                |   |
                  cfg.Nonterminal --+
                                    |
                                   Category

Known Subclasses:: GrammarCategory

A Category is a specialized feature structure, intended for use in parsing. It can act as a Nonterminal.

A Category differs from a FeatureStructure in these ways:

Categories may not be re-entrant.
Categories use value-based equality, while FeatureStructures use identity-based equality.
Strings in Categories are compared case-insensitively.
Categories have one feature marked as the 'head', which prints differently than other features if it has a value. For example, in the repr() representation of a Category, the head goes to the left, on the outside of the brackets. Subclasses of Category may change the feature name that is designated as the head, which is _head by default.
Subclasses of Category may contain a list of required features, which are names of features whose value is None if unspecified. A Category lacking a feature that is required in it will not unify with any Category that has that feature. If a required feature's value is None, it is considered to be not present. (Mixing different subclasses of Category is probably a bad idea.)
True and False are allowed as values. A feature named foo with a value of True is simply expressed as +foo. Similarly, if it is False, it is expressed as -foo.

Nested Classes

[hide private]

Inherited from featurestructure.FeatureStructure (private): _UnificationFailureError

Instance Methods

[hide private]

__init__(self, **features)
x.__init__(...) initializes x; see x.__class__.__doc__ for signature

source code

required_features(self)
Returns: A list of the names of all required features.

source code

__cmp__(self, other)

source code

Nonterminal

__div__(self, other)
Returns: A new Category based on this one, with its / feature set to other. source code

bool

__eq__(self, other)
Returns: True if self and other assign the same value to to every feature. source code

boolean

__ne__(self, other)
Returns: True if this non-terminal is not equal to other. source code

__hash__(self)
hash(x)

source code

freeze(self)
Freezing a Category memoizes its hash value, to make comparisons on it faster.

source code

bool

frozen(self)
Returns whether this Category is frozen (immutable).

source code

__setitem__(self, name, value)

source code

Category

symbol(self)
Returns: The node value corresponding to this Category. source code

str or None

head(self)
Returns: The head of this category (the value shown outside the brackets in its string representation).

source code

deepcopy(self, memo=None)
Returns: A deep copy of self. source code

list of FeatureStructure

reentrances(self)
Returns: A list of all feature structures that can be reached from self by multiple feature paths. source code

list of string

feature_names(self)
Returns: a list of all features that have values.

source code

get_feature(self, *args)

source code

has_feature(self, name)

source code

remove_unbound_vars(self)

source code

_remove_unbound_vars(self)

source code

_destructively_unify(self, other, bindings, trace=True, depth=0)
Attempt to unify self and other by modifying them in-place. source code

__repr__(self)
Returns: A string representation of this feature structure.

source code

_repr(self, reentrances, reentrance_ids)
Returns: A string representation of this feature structure.

source code

_str(self, reentrances, reentrance_ids)
Returns: A list of lines composing a string representation of this feature structure.

source code

Inherited from featurestructure.FeatureStructure: __getitem__, __str__, apply_bindings, equal_values, rename_variables, subsumes, unify

Inherited from featurestructure.FeatureStructure (private): _apply_bindings, _apply_forwards, _apply_forwards_to_bindings, _find_reentrances, _rebind_aliased_variables, _rename_variables

Inherited from object: __delattr__, __getattribute__, __new__, __reduce__, __reduce_ex__, __setattr__

Class Methods

[hide private]

_parseval(cls, s, position, reentrances)
Helper function that parses a feature value.

source code

_parse(cls, s, position=0, reentrances=None)
Helper function that parses a Category.

source code

parse_rules(cls, s)
Parse a CFG line involving Categories. source code

Inherited from featurestructure.FeatureStructure: parse

Class Variables

[hide private]

headname = '_head'

requiredFeatures = []

_PARSE_RE = {'arrow': re.compile(r'\s*->\s*'), 'assign': re.co...

k = 'reentrance'

v = re.compile(r'\s*->\s*')

Instance Variables

[hide private]

Inherited from featurestructure.FeatureStructure (private): _features, _forward

Inherited from cfg.Nonterminal (private): _symbol

Properties

[hide private]

Inherited from object: __class__

Method Details

[hide private]

init(self, **features)
(Constructor)

source code

x.__init__(...) initializes x; see x.__class__.__doc__ for signature

Overrides: featurestructure.FeatureStructure.__init__

required_features(self)

source code

Returns:: A list of the names of all required features.

cmp(self, other)
(Comparison operator)

source code

Overrides: cfg.Nonterminal.__cmp__

div(self, other)

source code

Returns: Nonterminal: A new Category based on this one, with its / feature set to other.
Overrides: cfg.Nonterminal.__div__

eq(self, other)
(Equality operator)

source code

Returns: bool: True if self and other assign the same value to to every feature. In particular, return true if self[p]==other[p] for every feature path p such that self[p] or other[p] is a base value (i.e., not a nested Category).
Overrides: featurestructure.FeatureStructure.__eq__

ne(self, other)

source code

Returns: boolean: True if this non-terminal is not equal to other. In particular, return true iff other is not a Nonterminal or this non-terminal's symbol is not equal to other's symbol.
Overrides: cfg.Nonterminal.__ne__: (inherited documentation)

hash(self)
(Hashing function)

source code

hash(x)

Overrides: featurestructure.FeatureStructure.__hash__

freeze(self)

source code

Freezing a Category memoizes its hash value, to make comparisons on it faster. After freezing, the Category and all its values are immutable.

Returns:: self

symbol(self)

source code

Returns: Category: The node value corresponding to this Category.
Overrides: cfg.Nonterminal.symbol

head(self)

source code

Returns: str or None: The head of this category (the value shown outside the brackets in its string representation). If there is no head, returns None.

deepcopy(self, memo=None)

source code

Returns:: A deep copy of self.
Overrides: featurestructure.FeatureStructure.deepcopy

reentrances(self)

source code

Returns: list of FeatureStructure: A list of all feature structures that can be reached from self by multiple feature paths.
Overrides: featurestructure.FeatureStructure.reentrances: (inherited documentation)

feature_names(self)

source code

Returns: list of string: a list of all features that have values.
Overrides: featurestructure.FeatureStructure.feature_names

_destructively_unify(self, other, bindings, trace=True, depth=0)

source code

Attempt to unify self and other by modifying them in-place. If the unification succeeds, then self will contain the unified value, and the value of other is undefined. If the unification fails, then a _UnificationFailureError is raised, and the values of self and other are undefined.

Overrides: featurestructure.FeatureStructure._destructively_unify: (inherited documentation)

repr(self)
(Representation operator)

source code

Display a single-line representation of this feature structure, suitable for embedding in other representations.

Returns:: A string representation of this feature structure.
Overrides: featurestructure.FeatureStructure.__repr__

_repr(self, reentrances, reentrance_ids)

source code

Returns:: A string representation of this feature structure.
Overrides: featurestructure.FeatureStructure._repr: (inherited documentation)

_str(self, reentrances, reentrance_ids)

source code

Returns:: A list of lines composing a string representation of this feature structure.
Overrides: featurestructure.FeatureStructure._str: (inherited documentation)

_parseval(cls, s, position, reentrances)
Class Method

source code

Helper function that parses a feature value. Currently supports: None, bools, integers, variables, strings, nested feature structures.

Parameters:

s - The string to parse.
position - The position in the string to start parsing.
reentrances - A dictionary from reentrance ids to values.

Returns:

A tuple (val, pos) of the value created by parsing and the position where the parsed value ends.

Overrides: featurestructure.FeatureStructure._parseval

_parse(cls, s, position=0, reentrances=None)
Class Method

source code

Helper function that parses a Category.

Parameters:

s - The string to parse.
position - The position in the string to start parsing.
reentrances - A dictionary from reentrance ids to values.

Returns:

A tuple (val, pos) of the feature structure created by parsing and the position where the parsed feature structure ends.

Overrides: featurestructure.FeatureStructure._parse

parse_rules(cls, s)
Class Method

source code

Parse a CFG line involving Categories. A line has this form:

lhs -> rhs | rhs | ...

where lhs is a Category, and each rhs is a sequence of Categories.

Returns:: a list of Productions, one for each rhs.

Class Variable Details

[hide private]

_PARSE_RE

Value:

{'arrow': re.compile(r'\s*->\s*'),
 'assign': re.compile(r'\s*=\s*'),
 'bool': re.compile(r'\s*([-\+])'),
 'bracket': re.compile(r'\s*\]\s*'),
 'categorystart': re.compile(r'\s*([^\s\(\)"\'-=,\[\]]*)\s*\['),
 'comma': re.compile(r'\s*,\s*'),
 'disjunct': re.compile(r'\s*\|\s*'),
 'ident': re.compile(r'\s*\((\d+)\)\s*'),
...

Class Category

__init__(self, **features) (Constructor)

required_features(self)

__cmp__(self, other) (Comparison operator)

__div__(self, other)

__eq__(self, other) (Equality operator)

__ne__(self, other)

__hash__(self) (Hashing function)

freeze(self)

symbol(self)

head(self)

deepcopy(self, memo=None)

reentrances(self)

feature_names(self)

_destructively_unify(self, other, bindings, trace=True, depth=0)

__repr__(self) (Representation operator)

_repr(self, reentrances, reentrance_ids)

_str(self, reentrances, reentrance_ids)

_parseval(cls, s, position, reentrances) Class Method

_parse(cls, s, position=0, reentrances=None) Class Method

parse_rules(cls, s) Class Method

_PARSE_RE

init(self, **features)
(Constructor)

cmp(self, other)
(Comparison operator)

div(self, other)

eq(self, other)
(Equality operator)

ne(self, other)

hash(self)
(Hashing function)

repr(self)
(Representation operator)

_parseval(cls, s, position, reentrances)
Class Method

_parse(cls, s, position=0, reentrances=None)
Class Method

parse_rules(cls, s)
Class Method