66 lines
2.2 KiB
Python
66 lines
2.2 KiB
Python
# Natural Language Toolkit: Parser API
|
|
#
|
|
# Copyright (C) 2001-2018 NLTK Project
|
|
# Author: Steven Bird <stevenbird1@gmail.com>
|
|
# Edward Loper <edloper@gmail.com>
|
|
# URL: <http://nltk.org/>
|
|
# For license information, see LICENSE.TXT
|
|
#
|
|
|
|
import itertools
|
|
|
|
from nltk.internals import overridden
|
|
|
|
class ParserI(object):
|
|
"""
|
|
A processing class for deriving trees that represent possible
|
|
structures for a sequence of tokens. These tree structures are
|
|
known as "parses". Typically, parsers are used to derive syntax
|
|
trees for sentences. But parsers can also be used to derive other
|
|
kinds of tree structure, such as morphological trees and discourse
|
|
structures.
|
|
|
|
Subclasses must define:
|
|
- at least one of: ``parse()``, ``parse_sents()``.
|
|
|
|
Subclasses may define:
|
|
- ``grammar()``
|
|
"""
|
|
def grammar(self):
|
|
"""
|
|
:return: The grammar used by this parser.
|
|
"""
|
|
raise NotImplementedError()
|
|
|
|
def parse(self, sent, *args, **kwargs):
|
|
"""
|
|
:return: An iterator that generates parse trees for the sentence.
|
|
When possible this list is sorted from most likely to least likely.
|
|
|
|
:param sent: The sentence to be parsed
|
|
:type sent: list(str)
|
|
:rtype: iter(Tree)
|
|
"""
|
|
if overridden(self.parse_sents):
|
|
return next(self.parse_sents([sent], *args, **kwargs))
|
|
elif overridden(self.parse_one):
|
|
return (tree for tree in [self.parse_one(sent, *args, **kwargs)] if tree is not None)
|
|
elif overridden(self.parse_all):
|
|
return iter(self.parse_all(sent, *args, **kwargs))
|
|
else:
|
|
raise NotImplementedError()
|
|
|
|
def parse_sents(self, sents, *args, **kwargs):
|
|
"""
|
|
Apply ``self.parse()`` to each element of ``sents``.
|
|
:rtype: iter(iter(Tree))
|
|
"""
|
|
return (self.parse(sent, *args, **kwargs) for sent in sents)
|
|
|
|
def parse_all(self, sent, *args, **kwargs):
|
|
""":rtype: list(Tree)"""
|
|
return list(self.parse(sent, *args, **kwargs))
|
|
|
|
def parse_one(self, sent, *args, **kwargs):
|
|
""":rtype: Tree or None"""
|
|
return next(self.parse(sent, *args, **kwargs), None)
|