def is_ltdict(obj):
    """
        ltd = {0:1,1:2,2:3}
        is_ltdict(ltd) == True
        ltd = {0:1,2:2,3:3}
        is_ltdict(ltd) == False
        ltd = {0:1,'1':2,2:3}
        is_ltdict(ltd) == False
    """
    if isinstance(obj, dict):
        pass
    else:
        return False
    index_set = set({})
    if obj == {}:
        return True
    else:
        for key in obj:
            if isinstance(key, int):
                if key >= 0:
                    index_set.add(key)
                else:
                    return False
            else:
                return False
        for i in range(0, obj.__len__()):
            if i in index_set:
                pass
            else:
                return False
        return True
