# Buggy code
def symbol_is_pair(
    market_symbol: str, base_currency: str = None, quote_currency: str = None
):
    """
    Check if the market symbol is a pair, i.e. that its symbol consists of the base currency and the
    quote currency separated by '/' character. If base_currency and/or quote_currency is passed,
    it also checks that the symbol contains appropriate base and/or quote currency part before
    and after the separating character correspondingly.
    """
    symbol_parts = market_symbol.split("/")
    return (
        len(symbol_parts) == 2
        and (
            symbol_parts[0] == base_currency
            if base_currency
            else len(symbol_parts[0]) > 0
        )
        and (
            symbol_parts[1] == quote_currency
            if quote_currency
            else len(symbol_parts[1]) > 0
        )
    )


# 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 symbol_is_pair(
    market_symbol: str, base_currency: str = None, quote_currency: str = None
) -> bool:
    """
    Check if the market symbol is a pair, i.e. that its symbol consists of the base currency and the
    quote currency separated by '/' character. If base_currency and/or quote_currency is passed,
    it also checks that the symbol contains appropriate base and/or quote currency part before
    and after the separating character correspondingly.
    """
    symbol_parts = market_symbol.split("/")
    return (
        len(symbol_parts) == 2
        and (
            symbol_parts[0] == base_currency
            if base_currency
            else len(symbol_parts[0]) > 0
        )
        and (
            symbol_parts[1] == quote_currency
            if quote_currency
            else len(symbol_parts[1]) > 0
        )
    )