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| | import itertools
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| | from nltk.internals import overridden
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| | class ParserI:
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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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