How to use the langdetect.utils.ngram.NGram.normalize_vi function in langdetect

def append(self, text):
        '''Append the target text for language detection.
        If the total size of target text exceeds the limit size specified by
        Detector.set_max_text_length(int), the rest is cut down.
        '''
        text = self.URL_RE.sub(' ', text)
        text = self.MAIL_RE.sub(' ', text)
        text = NGram.normalize_vi(text)
        pre = 0
        for i in xrange(min(len(text), self.max_text_length)):
            ch = text[i]
            if ch != ' ' or pre != ' ':
                self.text += ch
            pre = ch

def update(self, text):
        '''Update the language profile with (fragmented) text.
        Extract n-grams from text and add their frequency into the profile.
        '''
        if text is None:
            return
        text = NGram.normalize_vi(text)
        gram = NGram()
        for ch in text:
            gram.add_char(ch)
            for n in xrange(1, NGram.N_GRAM+1):
                self.add(gram.get(n))