spaCy/spacy/lemmatizer.py

147 lines
5.4 KiB
Python

from typing import Optional, Callable, List, Dict
from .lookups import Lookups
from .parts_of_speech import NAMES as UPOS_NAMES
class Lemmatizer:
"""
The Lemmatizer supports simple part-of-speech-sensitive suffix rules and
lookup tables.
DOCS: https://spacy.io/api/lemmatizer
"""
def __init__(
self,
lookups: Optional[Lookups] = None,
is_base_form: Optional[Callable] = None,
) -> None:
"""Initialize a Lemmatizer.
lookups (Lookups): The lookups object containing the (optional) tables
"lemma_rules", "lemma_index", "lemma_exc" and "lemma_lookup".
RETURNS (Lemmatizer): The newly constructed object.
"""
self.lookups = lookups if lookups is not None else Lookups()
self.is_base_form = is_base_form
def __call__(
self, string: str, univ_pos: str, morphology: Optional[dict] = None
) -> List[str]:
"""Lemmatize a string.
string (str): The string to lemmatize, e.g. the token text.
univ_pos (str / int): The token's universal part-of-speech tag.
morphology (dict): The token's morphological features following the
Universal Dependencies scheme.
RETURNS (list): The available lemmas for the string.
"""
lookup_table = self.lookups.get_table("lemma_lookup", {})
if "lemma_rules" not in self.lookups:
return [lookup_table.get(string, string)]
if isinstance(univ_pos, int):
univ_pos = UPOS_NAMES.get(univ_pos, "X")
univ_pos = univ_pos.lower()
if univ_pos in ("", "eol", "space"):
return [string.lower()]
# See Issue #435 for example of where this logic is requied.
if callable(self.is_base_form) and self.is_base_form(univ_pos, morphology):
return [string.lower()]
index_table = self.lookups.get_table("lemma_index", {})
exc_table = self.lookups.get_table("lemma_exc", {})
rules_table = self.lookups.get_table("lemma_rules", {})
if not any(
(
index_table.get(univ_pos),
exc_table.get(univ_pos),
rules_table.get(univ_pos),
)
):
if univ_pos == "propn":
return [string]
else:
return [string.lower()]
lemmas = self.lemmatize(
string,
index_table.get(univ_pos, {}),
exc_table.get(univ_pos, {}),
rules_table.get(univ_pos, []),
)
return lemmas
def noun(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "noun", morphology)
def verb(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "verb", morphology)
def adj(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "adj", morphology)
def det(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "det", morphology)
def pron(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "pron", morphology)
def adp(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "adp", morphology)
def num(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "num", morphology)
def punct(self, string: str, morphology: Optional[dict] = None) -> List[str]:
return self(string, "punct", morphology)
def lookup(self, string: str, orth: Optional[int] = None) -> str:
"""Look up a lemma in the table, if available. If no lemma is found,
the original string is returned.
string (str): The original string.
orth (int): Optional hash of the string to look up. If not set, the
string will be used and hashed.
RETURNS (str): The lemma if the string was found, otherwise the
original string.
"""
lookup_table = self.lookups.get_table("lemma_lookup", {})
key = orth if orth is not None else string
if key in lookup_table:
return lookup_table[key]
return string
def lemmatize(
self,
string: str,
index: Dict[str, List[str]],
exceptions: Dict[str, Dict[str, List[str]]],
rules: Dict[str, List[List[str]]],
) -> List[str]:
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 but preserve the ordering of applied "rules"
forms = list(dict.fromkeys(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