code: def _parse_date_columns(data_frame, parse_dates):
      
      parse_dates = _process_parse_dates_argument(parse_dates)
  
      # we want to coerce datetime64_tz dtypes for now to UTC
      # we could in theory do a 'nice' conversion from a FixedOffset tz
      # GH11216
      for col_name, df_col in data_frame.iteritems():
          if is_datetime64tz_dtype(df_col) or col_name in parse_dates:
              try:
                  fmt = parse_dates[col_name]
              except TypeError:
                  fmt = None
              data_frame[col_name] = _handle_date_column(df_col, format=fmt)
  
      return data_frame
docs: Force non-datetime columns to be read as such.
      Supports both string formatted and integer timestamp columns.