python开发---集合

Posted 2021-11-30 liuchunling

可变不可变：

可变：列表

不可变：字符串，数字，元组

访问顺序：

1.直接访问：数字

2.顺序访问：字符串，列表，元组

3.映射：字典

存放元素个数：

容器类型：列表，元组，字典

原子：数字，字符串

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集合：set

定义：由不同的元素组成的集合，集合是一种无序排列的可hash值，可以作为字典的key（只可存放不可变类型，即只能存放字符串，数字，元组）

定义集合：例：s = {1，2，3，4，5，6}

例：add() 添加
    s = {1,2,3,4,5,6}
    s.add("3")
    print(s)
    结果：{1, 2, 3, 4, 5, 6, ‘3‘}
例：clear()清空
例：copy()拷贝
例： pop()删除，随机删除
例： remov(),删除指定元素，元素不存在会报错
例：discard(),删除指定元素，元素不存在不会报错　

集合的关系

例：intersection(),交集   ==&
    ps = ["aa","bb","cc","dd"]
    ls = ["bb","cc","ee","ff"]
    p_s = set(ps)
    l_s = set(ls)
    print(p_s.intersection(l_s))   === print(p_s&l_s)
    结果：{‘bb‘, ‘cc‘}
例：union(),并集       ==|
    ps = ["aa","bb","cc","dd"]
    ls = ["bb","cc","ee","ff"]
    p_s = set(ps)
    l_s = set(ls) 
    print(p_s.union(l_s))          ===print(p_s|l_s)
    结果：{‘aa‘, ‘bb‘, ‘ee‘, ‘cc‘, ‘ff‘, ‘dd‘}
例：difference()，差集     ==-
    ps = ["aa","bb","cc","dd"]
    ls = ["bb","cc","ee","ff"]
    p_s = set(ps)
    l_s = set(ls)
    print(p_s-l_s)
    结果：{‘aa‘, ‘dd‘}
例：symmetric_difference(),交叉补集   ==^
    ps = ["aa","bb","cc","dd"]
    ls = ["bb","cc","ee","ff"]
    p_s = set(ps)
    l_s = set(ls)
    print(p_s.symmetric_difference(l_s))
    结果：{‘dd‘, ‘ff‘, ‘aa‘, ‘ee‘}

　

例：difference_update()，差集以后更改原数据
    ps = ["aa","bb","cc","dd"]
    ls = ["bb","cc","ee","ff"]
    p_s = set(ps)
    l_s = set(ls)
    p_s.difference_update(l_s)
    print(p_s)
    结果：{‘aa‘, ‘dd‘}
例：isdisjoint(),比较2个集合是否有交集，有交集返回False
例：issubset(),包含关系，s1是s2的子集返回True
例：issuperset(),包含关系，s1是s2的父集返回True    ===  >=
 

　　

字符串格式化---%或者format

1.format

1.%s传值（传任何值）

　　例：传单个值

　　print("i am %s my" %‘hhh‘)

　　 结果：i am hhh my

　　 例：传多个值

　　print(‘i am %s i love %s‘ % ("dl","maod"))

 　　结果：i am dl i love maod

2.%d传数字

3.%f传递浮点数（小数）默认小数点后保留6位

例：

　　tpl = "percent %f "% 8.8888

　　print(tpl)

　　结果：percent 8.888800

　　tpl = "prcent %0.3f "% 8.8888        ==保留小数点后3位

　　print(tpl)

　　结果：prcent 8.889 

4.%%打印百分号

5.sep

print("root","x","0","2",sep=":")
结果：root:x:0:2

6.%字典的传递

tpl = "i am %(name)s and age is %(age)d" % {"name": "dl","age": 18}
print(tpl)
结果：i am dl and age is 18

 

 

 

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