Package nltk :: Module cfg :: Class Nonterminal

Class Nonterminal

object --+
         |
        Nonterminal

Known Subclasses:

FeatStructNonterminal

A non-terminal symbol for a context free grammar. Nonterminal is a wrapper class for node values; it is used by Productions to distinguish node values from leaf values. The node value that is wrapped by a Nonterminal is known as its symbol. Symbols are typically strings representing phrasal categories (such as "NP" or "VP"). However, more complex symbol types are sometimes used (e.g., for lexicalized grammars). Since symbols are node values, they must be immutable and hashable. Two Nonterminals are considered equal if their symbols are equal.

See Also:: Grammar, Production

Instance Methods

[hide private]

__init__(self, symbol)
Construct a new non-terminal from the given symbol.

source code

(any)

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

boolean

__eq__(self, other)
Returns: True if this non-terminal is equal to other. source code

boolean

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

__cmp__(self, other)

source code

__hash__(self)
hash(x)

source code

string

__repr__(self)
Returns: A string representation for this Nonterminal. source code

string

__str__(self)
Returns: A string representation for this Nonterminal. source code

Nonterminal

__div__(self, rhs)
Returns: A new nonterminal whose symbol is A/B, where A is the symbol for this nonterminal, and B is the symbol for rhs. source code

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

Instance Variables

[hide private]

(any) _symbol
The node value corresponding to this Nonterminal.

Properties

[hide private]

Inherited from object: __class__

Method Details

[hide private]

init(self, symbol)
(Constructor)

source code

Construct a new non-terminal from the given symbol.

Parameters:

symbol ((any)) - The node value corresponding to this Nonterminal. This value must be immutable and hashable.

Overrides: object.__init__

symbol(self)

source code

Returns: (any): The node value corresponding to this Nonterminal.

eq(self, other)
(Equality operator)

source code

Returns: boolean: True if this non-terminal is equal to other. In particular, return true iff other is a Nonterminal and this non-terminal's symbol is equal to other's symbol.

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.

hash(self)
(Hashing function)

source code

hash(x)

Overrides: object.__hash__: (inherited documentation)

repr(self)
(Representation operator)

source code

repr(x)

Returns: string: A string representation for this Nonterminal. The string representation for a Nonterminal whose symbol is s is <s>.
Overrides: object.__repr__

str(self)
(Informal representation operator)

source code

str(x)

Returns: string: A string representation for this Nonterminal. The string representation for a Nonterminal whose symbol is s is s.
Overrides: object.__str__

div(self, rhs)

source code

Parameters:

rhs (Nonterminal) - The nonterminal used to form the right hand side of the new nonterminal.

Returns: Nonterminal

A new nonterminal whose symbol is A/B, where A is the symbol for this nonterminal, and B is the symbol for rhs.

Instance Variable Details

[hide private]

_symbol

The node value corresponding to this Nonterminal. This value must be immutable and hashable.

Type:: (any)

Class Nonterminal

__init__(self, symbol) (Constructor)

symbol(self)

__eq__(self, other) (Equality operator)

__ne__(self, other)

__hash__(self) (Hashing function)

__repr__(self) (Representation operator)

__str__(self) (Informal representation operator)

__div__(self, rhs)

_symbol

init(self, symbol)
(Constructor)

eq(self, other)
(Equality operator)

ne(self, other)

hash(self)
(Hashing function)

repr(self)
(Representation operator)

str(self)
(Informal representation operator)

div(self, rhs)