# Buggy code
def _ohlcv_load(
    self,
    pair: str,
    timeframe: str,
    timerange: Optional[TimeRange] = None,
) -> DataFrame:
    """
    Internal method used to load data for one pair from disk.
    Implements the loading and conversion to a Pandas dataframe.
    Timerange trimming and dataframe validation happens outside of this method.
    :param pair: Pair to load data
    :param timeframe: Ticker timeframe (e.g. "5m")
    :param timerange: Limit data to be loaded to this timerange.
                    Optionally implemented by subclasses to avoid loading
                    all data where possible.
    :return: DataFrame with ohlcv data, or empty DataFrame
    """
    filename = self._pair_data_filename(self._datadir, pair, timeframe)
    if not filename.exists():
        return DataFrame(columns=self._columns)
    pairdata = read_json(
        filename,
        orient="values",
        dtype={
            "open": "float",
            "high": "float",
            "low": "float",
            "close": "float",
            "volume": "float",
        },
    )
    pairdata.columns = self._columns
    pairdata["date"] = to_datetime(
        pairdata["date"], unit="ms", utc=True, infer_datetime_format=True
    )
    return pairdata


# 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 _ohlcv_load(
    self,
    pair: str,
    timeframe: str,
    timerange: Optional[TimeRange] = None,
) -> DataFrame:
    """
    Internal method used to load data for one pair from disk.
    Implements the loading and conversion to a Pandas dataframe.
    Timerange trimming and dataframe validation happens outside of this method.
    :param pair: Pair to load data
    :param timeframe: Ticker timeframe (e.g. "5m")
    :param timerange: Limit data to be loaded to this timerange.
                    Optionally implemented by subclasses to avoid loading
                    all data where possible.
    :return: DataFrame with ohlcv data, or empty DataFrame
    """
    filename = self._pair_data_filename(self._datadir, pair, timeframe)
    if not filename.exists():
        return DataFrame(columns=self._columns)
    pairdata = read_json(filename, orient="values")
    pairdata.columns = self._columns
    pairdata = pairdata.astype(
        dtype={
            "open": "float",
            "high": "float",
            "low": "float",
            "close": "float",
            "volume": "float",
        }
    )
    pairdata["date"] = to_datetime(
        pairdata["date"], unit="ms", utc=True, infer_datetime_format=True
    )
    return pairdata