# Buggy code
def parse_ticker_dataframe(
    ticker: list,
    timeframe: str,
    pair: str,
    *,
    fill_missing: bool = True,
    drop_incomplete: bool = True,
) -> DataFrame:
    """
    Converts a ticker-list (format ccxt.fetch_ohlcv) to a Dataframe
    :param ticker: ticker list, as returned by exchange.async_get_candle_history
    :param timeframe: timeframe (e.g. 5m). Used to fill up eventual missing data
    :param pair: Pair this data is for (used to warn if fillup was necessary)
    :param fill_missing: fill up missing candles with 0 candles
                         (see ohlcv_fill_up_missing_data for details)
    :param drop_incomplete: Drop the last candle of the dataframe, assuming it's incomplete
    :return: DataFrame
    """
    logger.debug("Parsing tickerlist to dataframe")
    cols = ["date", "open", "high", "low", "close", "volume"]
    frame = DataFrame(ticker, columns=cols)

    frame["date"] = to_datetime(
        frame["date"], unit="ms", utc=True, infer_datetime_format=True
    )

    # Some exchanges return int values for volume and even for ohlc.
    # Convert them since TA-LIB indicators used in the strategy assume floats
    # and fail with exception...
    frame = frame.astype(
        dtype={
            "open": "float",
            "high": "float",
            "low": "float",
            "close": "float",
            "volume": "float",
        }
    )

    # group by index and aggregate results to eliminate duplicate ticks
    frame = frame.groupby(by="date", as_index=False, sort=True).agg(
        {
            "open": "first",
            "high": "max",
            "low": "min",
            "close": "last",
            "volume": "max",
        }
    )
    # eliminate partial candle
    if drop_incomplete:
        frame.drop(frame.tail(1).index, inplace=True)
        logger.debug("Dropping last candle")

    if fill_missing:
        return ohlcv_fill_up_missing_data(frame, timeframe, pair)
    else:
        return frame


# Traceback (Exception)
2020-02-20 22:47:28,025 - freqtrade - ERROR - Fatal exception!
Traceback (most recent call last):
File "/opt/tradebot/freqtrade/.env/lib/python3.7/site-packages/talib/__init__.py", line 20, in wrapper
for arg in chain(args, kwargs.values())
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/freqtrade/freqtrade/main.py", line 36, in main
return_code = args['func'](args)
File "/freqtrade/freqtrade/commands/optimize_commands.py", line 76, in start_hyperopt
hyperopt.start()
File "/freqtrade/freqtrade/optimize/hyperopt.py", line 488, in start
preprocessed = self.backtesting.strategy.tickerdata_to_dataframe(data)
File "/freqtrade/freqtrade/strategy/interface.py", line 448, in tickerdata_to_dataframe
for pair, pair_data in tickerdata.items()}
File "/freqtrade/freqtrade/strategy/interface.py", line 448, in <dictcomp>
for pair, pair_data in tickerdata.items()}
File "/freqtrade/freqtrade/strategy/interface.py", line 464, in advise_indicators
return self.populate_indicators(dataframe, metadata)
File "/freqtrade/user_data/strategies/MyDev.py", line 205, in populate_indicators
dataframe['mfi'] = ta.MFI(dataframe)
File "talib/_abstract.pxi", line 352, in talib._ta_lib.Function.__call__
File "talib/_abstract.pxi", line 383, in talib._ta_lib.Function.__call_function
File "/opt/tradebot/freqtrade/.env/lib/python3.7/site-packages/talib/__init__.py", line 24, in wrapper
return func(*args, **kwargs)
File "talib/_func.pxi", line 8454, in talib._ta_lib.MFI
Exception: volume is not double

# Fixed code
def parse_ticker_dataframe(
    ticker: list,
    timeframe: str,
    pair: str,
    *,
    fill_missing: bool = True,
    drop_incomplete: bool = True,
) -> DataFrame:
    """
    Converts a ticker-list (format ccxt.fetch_ohlcv) to a Dataframe
    :param ticker: ticker list, as returned by exchange.async_get_candle_history
    :param timeframe: timeframe (e.g. 5m). Used to fill up eventual missing data
    :param pair: Pair this data is for (used to warn if fillup was necessary)
    :param fill_missing: fill up missing candles with 0 candles
                         (see ohlcv_fill_up_missing_data for details)
    :param drop_incomplete: Drop the last candle of the dataframe, assuming it's incomplete
    :return: DataFrame
    """
    logger.debug("Parsing tickerlist to dataframe")
    cols = DEFAULT_DATAFRAME_COLUMNS
    frame = DataFrame(ticker, columns=cols)

    frame["date"] = to_datetime(
        frame["date"], unit="ms", utc=True, infer_datetime_format=True
    )

    # Some exchanges return int values for volume and even for ohlc.
    # Convert them since TA-LIB indicators used in the strategy assume floats
    # and fail with exception...
    frame = frame.astype(
        dtype={
            "open": "float",
            "high": "float",
            "low": "float",
            "close": "float",
            "volume": "float",
        }
    )
    return clean_ohlcv_dataframe(
        frame,
        timeframe,
        pair,
        fill_missing=fill_missing,
        drop_incomplete=drop_incomplete,
    )