我需要写代码阅读所有的文本文件在子文件夹和计数的频率在每个文本文件中的一些单词。下面是我的编码：

def process_files(dir):
    # List of filenames in the directory
    
    filenames = []
    for root, _, files in walk(dir):
        filenames.extend([join(root, file) for file in filter(files, '*.txt')])
    
    df = pd.DataFrame()

    for filename in filenames:
        virtual_currency, bitcoin,blockchain, cryptocurrency, digital_currency, litecoin, dogecoin, etherrum =0, 0, 0, 0, 0, 0, 0,0

        with open(filename, 'r') as f:
            contents = f.read().lower()
            
        # Process the content
            cryptocurrency=contents.count("cryptocurrenc")
            virtual_currency = contents.count("virtual currenc")
            digital_currency=contents.count("digital currenc")
            bitcoin = contents.count("bitcoin")
            blockchain=contents.count("blockchain")
            litecoin=contents.count("litecoin")
            dogecoin=contents.count("dogecoin")
            etherrum=contents.count("etherrum")
        
        # Create data row
            data = {'File Name': filename,
            'Virtual Currency': virtual_currency,
            'Bitcoin': bitcoin,
            'cryptocurrency': cryptocurrency,
            'digital currency': digital_currency,
            'litecoin': litecoin,
            'dogecoin': dogecoin,
            'etherrum': etherrum}

        #df.append(data,ignore_index=True)
        
            a=pd.DataFrame(data, index=[0])
            df=df.append(a,ignore_index=True, sort=False)
        
        # Save data to CSV
        df.to_csv(os.path.join(dir, filename), index=False)

    return df

result = process_files(r'C:\test\QTR2')

字符串
问题是，每个文档的生成结果都是相同的。我的猜测是，最后的结果改写了旧的值。

的数据
谁能帮我检查一下是哪一部分出了问题？我真的很感激你能提供的任何帮助。