<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def best(self):
        '''
        Return current 'best' choice of bandit.

        Returns
        -------
        int
            Index of bandit
        '''

        if len(self.choices) < 1:
            print('slots: No trials run so far.')
            return None
        else:
            return np.argmax(self.wins/(self.pulls+0.1))