nltk.sem.drt module

exception nltk.sem.drt.AnaphoraResolutionException

Bases: Exception

class nltk.sem.drt.DRS

Bases: DrtExpression, Expression

A Discourse Representation Structure.

__init__(refs, conds, consequent=None)

Parameters:

• refs – list of DrtIndividualVariableExpression for the discourse referents

• conds – list of Expression for the conditions

eliminate_equality()

fol()

free()

See:

Expression.free()

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

replace(variable, expression, replace_bound=False, alpha_convert=True)

Replace all instances of variable v with expression E in self, where v is free in self.

visit(function, combinator)

See:

Expression.visit()

visit_structured(function, combinator)

See:

Expression.visit_structured()

class nltk.sem.drt.DrsDrawer

Bases: object

BUFFER = 3

OUTERSPACE = 6

TOPSPACE = 10

__init__(drs, size_canvas=True, canvas=None)

Parameters:

• drs – DrtExpression, The DRS to be drawn

• size_canvas – bool, True if the canvas size should be the exact size of the DRS

• canvas – Canvas The canvas on which to draw the DRS. If none is given, create a new canvas.

draw(x=6, y=10)

Draw the DRS

class nltk.sem.drt.DrtAbstractVariableExpression

Bases: DrtExpression, AbstractVariableExpression

eliminate_equality()

fol()

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

class nltk.sem.drt.DrtApplicationExpression

Bases: DrtExpression, ApplicationExpression

fol()

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

class nltk.sem.drt.DrtBinaryExpression

Bases: DrtExpression, BinaryExpression

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

class nltk.sem.drt.DrtBooleanExpression

Bases: DrtBinaryExpression, BooleanExpression

class nltk.sem.drt.DrtConcatenation

Bases: DrtBooleanExpression

DRS of the form ‘(DRS + DRS)’

__init__(first, second, consequent=None)

eliminate_equality()

fol()

getOp()

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

replace(variable, expression, replace_bound=False, alpha_convert=True)

Replace all instances of variable v with expression E in self, where v is free in self.

simplify()

Returns:

beta-converted version of this expression

visit(function, combinator)

See:

Expression.visit()

class nltk.sem.drt.DrtConstantExpression

Bases: DrtAbstractVariableExpression, ConstantExpression

class nltk.sem.drt.DrtEqualityExpression

Bases: DrtBinaryExpression, EqualityExpression

fol()

class nltk.sem.drt.DrtEventVariableExpression

Bases: DrtIndividualVariableExpression, EventVariableExpression

class nltk.sem.drt.DrtExpression

Bases: object

This is the base abstract DRT Expression from which every DRT Expression extends.

applyto(other)

draw()

eliminate_equality()

equiv(other, prover=None)

Check for logical equivalence. Pass the expression (self <-> other) to the theorem prover. If the prover says it is valid, then the self and other are equal.

Parameters:

• other – an DrtExpression to check equality against

• prover – a nltk.inference.api.Prover

classmethod fromstring(s)

get_refs(recursive=False)

Return the set of discourse referents in this DRS. :param recursive: bool Also find discourse referents in subterms? :return: list of Variable objects

is_pronoun_function()

Is self of the form “PRO(x)”?

make_EqualityExpression(first, second)

make_VariableExpression(variable)

pretty_format()

Draw the DRS :return: the pretty print string

pretty_print()

resolve_anaphora()

property type

typecheck(signature=None)

class nltk.sem.drt.DrtFunctionVariableExpression

Bases: DrtAbstractVariableExpression, FunctionVariableExpression

class nltk.sem.drt.DrtIndividualVariableExpression

Bases: DrtAbstractVariableExpression, IndividualVariableExpression

class nltk.sem.drt.DrtLambdaExpression

Bases: DrtExpression, LambdaExpression

alpha_convert(newvar)

Rename all occurrences of the variable introduced by this variable binder in the expression to newvar. :param newvar: Variable, for the new variable

fol()

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

class nltk.sem.drt.DrtNegatedExpression

Bases: DrtExpression, NegatedExpression

fol()

get_refs(recursive=False)

See:

AbstractExpression.get_refs()

class nltk.sem.drt.DrtOrExpression

Bases: DrtBooleanExpression, OrExpression

fol()

class nltk.sem.drt.DrtParser

Bases: LogicParser

A lambda calculus expression parser.

__init__()

Parameters:

type_check (bool) – should type checking be performed to their types?

get_BooleanExpression_factory(tok)

This method serves as a hook for other logic parsers that have different boolean operators

get_all_symbols()

This method exists to be overridden

handle(tok, context)

This method is intended to be overridden for logics that use different operators or expressions

handle_DRS(tok, context)

handle_conds(context)

handle_prop(tok, context)

handle_refs()

isvariable(tok)

make_ApplicationExpression(function, argument)

make_BooleanExpression(factory, first, second)

make_EqualityExpression(first, second)

This method serves as a hook for other logic parsers that have different equality expression classes

make_LambdaExpression(variables, term)

make_NegatedExpression(expression)

make_VariableExpression(name)

class nltk.sem.drt.DrtProposition

Bases: DrtExpression, Expression

__init__(variable, drs)

eliminate_equality()

fol()

get_refs(recursive=False)

Return the set of discourse referents in this DRS. :param recursive: bool Also find discourse referents in subterms? :return: list of Variable objects

replace(variable, expression, replace_bound=False, alpha_convert=True)

Replace every instance of ‘variable’ with ‘expression’ :param variable: Variable The variable to replace :param expression: Expression The expression with which to replace it :param replace_bound: bool Should bound variables be replaced? :param alpha_convert: bool Alpha convert automatically to avoid name clashes?

visit(function, combinator)

See:

Expression.visit()

visit_structured(function, combinator)

See:

Expression.visit_structured()

class nltk.sem.drt.DrtTokens

Bases: Tokens

CLOSE_BRACKET = ']'

COLON = ':'

DRS = 'DRS'

DRS_CONC = '+'

OPEN_BRACKET = '['

PRONOUN = 'PRO'

PUNCT = ['+', '[', ']', ':']

SYMBOLS = ['&', '^', '|', '->', '=>', '<->', '<=>', '=', '==', '!=', '\\', '.', '(', ')', ',', '-', '!', '+', '[', ']', ':']

TOKENS = ['and', '&', '^', 'or', '|', 'implies', '->', '=>', 'iff', '<->', '<=>', '=', '==', '!=', 'some', 'exists', 'exist', 'all', 'forall', 'iota', '\\', '.', '(', ')', ',', 'not', '-', '!', 'DRS', '+', '[', ']', ':']

nltk.sem.drt.DrtVariableExpression(variable)

This is a factory method that instantiates and returns a subtype of DrtAbstractVariableExpression appropriate for the given variable.

class nltk.sem.drt.PossibleAntecedents

Bases: list, DrtExpression, Expression

free()

Set of free variables.

replace(variable, expression, replace_bound=False, alpha_convert=True)

Replace all instances of variable v with expression E in self, where v is free in self.

nltk.sem.drt.demo()

nltk.sem.drt.resolve_anaphora(expression, trail=[])

nltk.sem.drt.test_draw()