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120 lines
4.3 KiB
Python
120 lines
4.3 KiB
Python
# coding: utf8
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from __future__ import unicode_literals
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from .symbols import POS, NOUN, VERB, ADJ, PUNCT, PROPN
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from .symbols import VerbForm_inf, VerbForm_none, Number_sing, Degree_pos
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class Lemmatizer(object):
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@classmethod
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def load(cls, path, index=None, exc=None, rules=None, lookup=None):
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return cls(index, exc, rules, lookup)
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def __init__(self, index=None, exceptions=None, rules=None, lookup=None):
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self.index = index
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self.exc = exceptions
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self.rules = rules
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self.lookup_table = lookup if lookup is not None else {}
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def __call__(self, string, univ_pos, morphology=None):
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if not self.rules:
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return [self.lookup_table.get(string, string)]
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if univ_pos in (NOUN, 'NOUN', 'noun'):
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univ_pos = 'noun'
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elif univ_pos in (VERB, 'VERB', 'verb'):
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univ_pos = 'verb'
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elif univ_pos in (ADJ, 'ADJ', 'adj'):
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univ_pos = 'adj'
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elif univ_pos in (PUNCT, 'PUNCT', 'punct'):
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univ_pos = 'punct'
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elif univ_pos in (PROPN, 'PROPN'):
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return [string]
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else:
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return [string.lower()]
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# See Issue #435 for example of where this logic is requied.
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if self.is_base_form(univ_pos, morphology):
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return [string.lower()]
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lemmas = lemmatize(string, self.index.get(univ_pos, {}),
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self.exc.get(univ_pos, {}),
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self.rules.get(univ_pos, []))
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return lemmas
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def is_base_form(self, univ_pos, morphology=None):
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"""
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Check whether we're dealing with an uninflected paradigm, so we can
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avoid lemmatization entirely.
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"""
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morphology = {} if morphology is None else morphology
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others = [key for key in morphology
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if key not in (POS, 'Number', 'POS', 'VerbForm', 'Tense')]
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if univ_pos == 'noun' and morphology.get('Number') == 'sing':
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return True
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elif univ_pos == 'verb' and morphology.get('VerbForm') == 'inf':
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return True
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# This maps 'VBP' to base form -- probably just need 'IS_BASE'
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# morphology
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elif univ_pos == 'verb' and (morphology.get('VerbForm') == 'fin' and
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morphology.get('Tense') == 'pres' and
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morphology.get('Number') is None and
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not others):
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return True
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elif univ_pos == 'adj' and morphology.get('Degree') == 'pos':
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return True
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elif VerbForm_inf in morphology:
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return True
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elif VerbForm_none in morphology:
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return True
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elif Number_sing in morphology:
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return True
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elif Degree_pos in morphology:
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return True
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else:
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return False
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def noun(self, string, morphology=None):
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return self(string, 'noun', morphology)
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def verb(self, string, morphology=None):
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return self(string, 'verb', morphology)
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def adj(self, string, morphology=None):
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return self(string, 'adj', morphology)
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def punct(self, string, morphology=None):
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return self(string, 'punct', morphology)
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def lookup(self, string):
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if string in self.lookup_table:
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return self.lookup_table[string]
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return string
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def lemmatize(string, index, exceptions, rules):
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orig = string
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string = string.lower()
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forms = []
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oov_forms = []
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for old, new in rules:
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if string.endswith(old):
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form = string[:len(string) - len(old)] + new
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if not form:
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pass
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elif form in index or not form.isalpha():
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forms.append(form)
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else:
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oov_forms.append(form)
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# Remove duplicates, and sort forms generated by rules alphabetically.
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forms = list(set(forms))
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# Put exceptions at the front of the list, so they get priority.
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# This is a dodgy heuristic -- but it's the best we can do until we get
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# frequencies on this. We can at least prune out problematic exceptions,
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# if they shadow more frequent analyses.
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for form in exceptions.get(string, []):
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if form not in forms:
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forms.insert(0, form)
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if not forms:
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forms.extend(oov_forms)
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if not forms:
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forms.append(orig)
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return forms
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