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# Natural Language Toolkit: Parser API
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#
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# Copyright (C) 2001-2020 NLTK Project
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# Author: Steven Bird <stevenbird1@gmail.com>
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# Edward Loper <edloper@gmail.com>
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# URL: <http://nltk.org/>
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# For license information, see LICENSE.TXT
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#
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import itertools
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from nltk.internals import overridden
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class ParserI(object):
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"""
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A processing class for deriving trees that represent possible
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structures for a sequence of tokens. These tree structures are
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known as "parses". Typically, parsers are used to derive syntax
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trees for sentences. But parsers can also be used to derive other
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kinds of tree structure, such as morphological trees and discourse
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structures.
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Subclasses must define:
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- at least one of: ``parse()``, ``parse_sents()``.
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Subclasses may define:
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- ``grammar()``
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"""
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def grammar(self):
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"""
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:return: The grammar used by this parser.
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"""
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raise NotImplementedError()
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def parse(self, sent, *args, **kwargs):
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"""
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:return: An iterator that generates parse trees for the sentence.
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When possible this list is sorted from most likely to least likely.
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:param sent: The sentence to be parsed
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:type sent: list(str)
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:rtype: iter(Tree)
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"""
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if overridden(self.parse_sents):
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return next(self.parse_sents([sent], *args, **kwargs))
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elif overridden(self.parse_one):
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return (
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tree
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for tree in [self.parse_one(sent, *args, **kwargs)]
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if tree is not None
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)
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elif overridden(self.parse_all):
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return iter(self.parse_all(sent, *args, **kwargs))
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else:
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raise NotImplementedError()
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def parse_sents(self, sents, *args, **kwargs):
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"""
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Apply ``self.parse()`` to each element of ``sents``.
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:rtype: iter(iter(Tree))
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"""
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return (self.parse(sent, *args, **kwargs) for sent in sents)
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def parse_all(self, sent, *args, **kwargs):
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""":rtype: list(Tree)"""
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return list(self.parse(sent, *args, **kwargs))
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def parse_one(self, sent, *args, **kwargs):
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""":rtype: Tree or None"""
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return next(self.parse(sent, *args, **kwargs), None)
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