词干提取

import nltk.stem.porter as pt
import nltk.stem.lancaster as lc
import nltk.stem.snowball as sb

# 波特词干提取器  (偏宽松)
stemmer = pt.PorterStemmer()
# 朗卡斯特词干提取器   (偏严格)
stemmer = lc.LancasterStemmer()
# 思诺博词干提取器   (偏中庸)
stemmer = sb.SnowballStemmer('english')
r = stemmer.stem('playing') # 词干提取

词性还原

与词干提取作用类似, 次干提取出的词干信息不利于人工二次处理(人读不懂), 词性还原可以把名词复数等形式恢复为单数形式. 更有利于人工二次处理.

import nltk.stem as ns
# 词性还原器
lemmatizer = ns.WordNetLemmatizer()
n_lemm=lemmatizer.lemmatize(word, pos='n')
v_lemm=lemmatizer.lemmatize(word, pos='v')

案例：词干提取

"""
词干提取器 
"""
import nltk.stem.porter as pt
import nltk.stem.lancaster as lc
import nltk.stem.snowball as sb

words = ['table', 'probably', 'wolves', 
	'playing', 'is', 'the', 'beaches', 
	'grouded', 'dreamt', 'envision']

pt_stemmer = pt.PorterStemmer()
lc_stemmer = lc.LancasterStemmer()
sb_stemmer = sb.SnowballStemmer('english')

for word in words:
	pt_stem = pt_stemmer.stem(word)
	lc_stem = lc_stemmer.stem(word)
	sb_stem = sb_stemmer.stem(word)
	print('%8s %8s %8s %8s' % \
		  (word, pt_stem, lc_stem, sb_stem))

提取的结果：

   table     tabl     tabl     tabl
probably  probabl     prob  probabl
  wolves     wolv     wolv     wolv
 playing     play     play     play
      is       is       is       is
     the      the      the      the
 beaches    beach    beach    beach
 grouded    groud    groud    groud
  dreamt   dreamt   dreamt   dreamt
envision    envis    envid    envis

案例：词性还原

"""
词性还原
"""
import nltk.stem as ns
import nltk
nltk.download('wordnet')

words = ['table', 'probably', 'wolves', 
	'playing', 'is', 'the', 'beaches', 
	'grouded', 'dreamt', 'envision']

lemmatizer = ns.WordNetLemmatizer()
for word in words:
	n_lemm = lemmatizer.lemmatize(word,pos='n')
	v_lemm = lemmatizer.lemmatize(word,pos='v')
	print('%8s %8s %8s' % \
		  (word, n_lemm, v_lemm))

如下是词性还原的结果：

 table    table    table
probably probably probably
  wolves     wolf   wolves
 playing  playing     play
      is       is       be
     the      the      the
 beaches    beach    beach
 grouded  grouded  grouded
  dreamt   dreamt    dream
envision envision envision