# Buggy code
def _init_ccxt(
    self, exchange_config: dict, ccxt_module=ccxt, ccxt_kwargs: dict = None
) -> ccxt.Exchange:
    """
    Initialize ccxt with given config and return valid
    ccxt instance.
    """
    # Find matching class for the given exchange name
    name = exchange_config["name"]

    if not is_exchange_known_ccxt(name, ccxt_module):
        raise OperationalException(f"Exchange {name} is not supported by ccxt")

    ex_config = {
        "apiKey": exchange_config.get("key"),
        "secret": exchange_config.get("secret"),
        "password": exchange_config.get("password"),
        "uid": exchange_config.get("uid", ""),
    }
    if ccxt_kwargs:
        logger.info("Applying additional ccxt config: %s", ccxt_kwargs)
        ex_config.update(ccxt_kwargs)
    try:
        api = getattr(ccxt_module, name.lower())(ex_config)
    except (KeyError, AttributeError) as e:
        raise OperationalException(f"Exchange {name} is not supported") from e
    except ccxt.BaseError as e:
        raise OperationalException(f"Initialization of ccxt failed. Reason: {e}") from e

    self.set_sandbox(api, exchange_config, name)

    return api


# 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 _init_ccxt(
    self,
    exchange_config: Dict[str, Any],
    ccxt_module: CcxtModuleType = ccxt,
    ccxt_kwargs: dict = None,
) -> ccxt.Exchange:
    """
    Initialize ccxt with given config and return valid
    ccxt instance.
    """
    # Find matching class for the given exchange name
    name = exchange_config["name"]

    if not is_exchange_known_ccxt(name, ccxt_module):
        raise OperationalException(f"Exchange {name} is not supported by ccxt")

    ex_config = {
        "apiKey": exchange_config.get("key"),
        "secret": exchange_config.get("secret"),
        "password": exchange_config.get("password"),
        "uid": exchange_config.get("uid", ""),
    }
    if ccxt_kwargs:
        logger.info("Applying additional ccxt config: %s", ccxt_kwargs)
        ex_config.update(ccxt_kwargs)
    try:
        api = getattr(ccxt_module, name.lower())(ex_config)
    except (KeyError, AttributeError) as e:
        raise OperationalException(f"Exchange {name} is not supported") from e
    except ccxt.BaseError as e:
        raise OperationalException(f"Initialization of ccxt failed. Reason: {e}") from e

    self.set_sandbox(api, exchange_config, name)

    return api