The problem is that you're trying to append data to `final_dataframe` using `_append`, which doesn't work because it's not designed for appending rows.

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Why pd.concat Doesn't Behave as Expected When Appending a Series with an Index Matching Columns

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How to Import Multiple CSV Files into Different Dataframes with Python 3.6 and Rename Them Based on File Names

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Splitting Strings in a Pandas DataFrame: A Step-by-Step Guide to Extracting Specific Values