spaCy/spacy/lemmatizer.py
2018-07-05 13:56:02 +02:00

120 lines
4.3 KiB
Python

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