code: def _remove_nonascii(self, df):
      
  
      df_copy = df.copy(deep=True)
      for col in df_copy.columns:
        if (df_copy[col].dtype == np.dtype('O')):
          df_copy[col] = df[col].apply(
            lambda x: re.sub(r'[^\x00-\x7f]', r'', x) if isinstance(x, six.string_types) else x)
  
      return df_copy
docs: Make copy and remove non-ascii characters from it.