(list1, list2)
return ret
list1: previous
    list2: current
    
    return: intersection(previous & current) / current
list1: previous
    list2: current
    
    return: intersection(previous & current) / current
list1 : previous list2 : current return : intersection ( previous & current ) / current
def ratio(list1, list2):
    """
    list1: previous
    list2: current
    
    return: intersection(previous & current) / current
    """
    if len(list1)==0 or len(list2)==0:
        return 
    ret = sum([1 for i in list2 if i in list1]) / len(list2)
    
    return ret
def ratio ( list1 , list2 ) : if len ( list1 ) == 0 or len ( list2 ) == 0 : return ret = sum ( [ 1 for i in list2 if i in list1 ] ) / len ( list2 ) return ret