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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clean_df(df, header=None, **read_csv_kwargs):
 """ Convert UTF8 characters in a CSV file or dataframe into ASCII Args: df (DataFrame or str):
 DataFrame or path or url to CSV """

    df = read_csv(df, header=header, **read_csv_kwargs)
    df = df.fillna(' ')
    for col in df.columns:
        df[col] = df[col].apply(unicode2ascii)
    return df