Python自定义函数输出结果是形参

如题，自定义了函数，想要实现分词并统计单词数功能。但是输出结果不是实参而是形参

def SenLen(sen1):
    sen1 = 'a b c.'
    import re,string
    punc = '~`!#$%^&*()_+-=|\';":/.,?><~·！@#￥%……&*（）——+-=“：’；、。，？》《{}'
    sen2 = (re.sub(r"[%s]+" % punc, "", sen1))
    import nltk
    Words = nltk.word_tokenize(sen2)
    print(len(Words))
text = '''“ The teacher said that that that that that boy used in the composition is the right teachers”'''
SenLen(text)

###### 输出的结果是3，而不是实参里的17