# Buggy code
def fetch_ticker(self, pair: str, refresh: Optional[bool] = True) -> dict:
    if refresh or pair not in self._cached_ticker.keys():
        try:
            if pair not in self._api.markets or not self._api.markets[pair].get(
                "active"
            ):
                raise DependencyException(f"Pair {pair} not available")
            data = self._api.fetch_ticker(pair)
            try:
                self._cached_ticker[pair] = {
                    "bid": float(data["bid"]),
                    "ask": float(data["ask"]),
                }
            except KeyError:
                logger.debug("Could not cache ticker data for %s", pair)
            return data
        except (ccxt.NetworkError, ccxt.ExchangeError) as e:
            raise TemporaryError(
                f"Could not load ticker due to {e.__class__.__name__}. Message: {e}"
            ) from e
        except ccxt.BaseError as e:
            raise OperationalException(e) from e
    else:
        logger.info("returning cached ticker-data for %s", pair)
        return self._cached_ticker[pair]


# 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 fetch_ticker(self, pair: str) -> dict:
    try:
        if pair not in self._api.markets or not self._api.markets[pair].get("active"):
            raise DependencyException(f"Pair {pair} not available")
        data = self._api.fetch_ticker(pair)
        return data
    except (ccxt.NetworkError, ccxt.ExchangeError) as e:
        raise TemporaryError(
            f"Could not load ticker due to {e.__class__.__name__}. Message: {e}"
        ) from e
    except ccxt.BaseError as e:
        raise OperationalException(e) from e