Python stem函数错误：stem需要一个位置参数

这里的stem函数显示了一个错误，表示stem在循环中需要一个位置参数，如所讨论的那个样

from nltk.stem import PorterStemmer as ps 

text='my name is pythonly and looking for a pythonian group to be formed by me iteratively'

words = word_tokenize(text)

for word in words:
    print(ps.stem(word))

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您需要实例化PorterStemmer对象

from nltk.stem import PorterStemmer as ps
from nltk.tokenize import word_tokenize

stemmer = ps()

text = 'my name is pythonly and looking for a pythonian group to be formed by me iteratively'
words = word_tokenize(text)
for t in words:
    print(t, stemmer.stem(t))

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但是，如果我使用ps.stem（i）而不是stemmer=ps（），然后运行“print（ps.stem（i）”，为什么会显示错误