python——深浅copy

赋值运算，对于赋值运算来说，元素用的都是一个内存地址
    s = ["1","2","3"]
    b = s
    s.append("4")
    print(s,b)#打印['1', '2', '3', '4'] ['1', '2', '3', '4']
    s = ["1","2","3",[11,22,33]]
    b = s
    s[-1].append("4")
    print(s, b)#打印['1', '2', '3', [11, 22, 33, '4']] ['1', '2', '3', [11, 22, 33, '4']]
浅copy，第一层元素各自独立，第二层开始，公用一个内存地址
    s = ["1","2","3"]
    b = s.copy()
    s.append("4")
    print(s,b)#打印['1', '2', '3', '4'] ['1', '2', '3']
    s = ["1","2","3",[11,22,33]]
    b = s.copy()
    s[-1].append("4")
    print(s,b)#打印['1', '2', '3', [11, 22, 33, '4']] ['1', '2', '3', [11, 22, 33, '4']]
    print(id(s),id(b))#打印2491607516992 2491607677824，两个不同的内存地址
    print(id(s[-1]),id(b[-1]))#打印1488448126720 1488448126720，第二层元素开始内存地址相同
深copy，引用copy模块,每层的元素都是独立的
    import copy
    s = ["1","2","3",[11,22,33]]
    b = copy.deepcopy(s)
    s[-1].append("4")
    print(s,b)#打印['1', '2', '3', [11, 22, 33, '4']] ['1', '2', '3', [11, 22, 33]]
切片来说，都是浅copy
    s = ["1","2","3",[11,22,33]]
    b = s[:]
    s[-1].append("4")
    print(s,b)#打印['1', '2', '3', [11, 22, 33, '4']] ['1', '2', '3', [11, 22, 33, '4']]