'Attempt to find a unique asset whose symbol is the given string.
If multiple assets have held the given symbol, return a 0.
If no asset has held the given symbol, return a  NaN.'

def _lookup_unconflicted_symbol(self, symbol):

    try:
        uppered = symbol.upper()
    except AttributeError:
        return numpy.nan
    try:
        return self.finder.lookup_symbol(uppered, as_of_date=None)
    except MultipleSymbolsFound:
        return 0
    except SymbolNotFound:
        return numpy.nan
