Python学习（五）—— 集合和字符格式化

数据类型和变量的总结

字符串

数字

列表

元组

字典

分类

1、可变不可变：

可变（即修改变量值以后id不改变）：列表、字典

不可变（即修改变量值以后id改变）：字符串、数字、元组

2、访问顺序：

直接访问：数字

顺序访问：字符串、列表、元组

映射访问：字典

3、存放元素个数：

容器类型：列表、元组、字典

原子类型：数字、字符串

集合

定义：由不同元素组成的集合，集合中是一组无序排列的可hash值（元素必须都是不可变类型：字符串、数字、元组），可以作为字典的key

特点：集合的目的是将不同值存放在一起，不同的集合间用"，"分开

 s = {1,3,5,2,6,5}
 print(s)
 #{1, 2, 3, 5, 6}
 for i in s:
     print(i)
 """
 1
 2
 3
 5
 6
 """
 s1 = set("alexx")
 print(s1)
 #{'l', 'a', 'x', 'e'}

注意set()定义的使用方式：

 s2 = set(["alex","alex","sb"])
 #s2 = set("alex","alex","sb")=>Wrong
 print(s2)
 #{'alex', 'sb'}

注意：另一种定义方式可以将集合定义为不可变类型

 s = frozenset("hello")
 print(s)
 #frozenset({'e', 'o', 'l', 'h'})

集合的运算关系

.intersection()    &

求交集

 1 English = ["Lily", "Sally", "Tom", "Paul"]
 2 Math = ["Lily", "Sally", "John"]
 3 English_s = set(English)
 4 Math_s = set(Math)
 5 print(English_s, Math_s)
 6 print(English_s.intersection(Math_s))
 7 """
 8 {'Sally', 'Paul', 'Lily', 'Tom'} {'Sally', 'Lily', 'John'}
 9 {'Sally', 'Lily'}
10 """

.union()      |

求并集

1 English = ["Lily", "Sally", "Tom", "Paul"]
2 Math = ["Lily", "Sally", "John"]
3 English_s = set(English)
4 Math_s = set(Math)
5 print(English_s|Math_s)
6 """
7 {'Sally', 'Paul', 'John', 'Tom', 'Lily'}
8 """

.difference()    -

求差集

1 Math = ["Lily", "Sally", "John"]
2 English_s = set(English)
3 Math_s = set(Math)
4 print(English_s-Math_s)
5 print(Math_s-English_s)
6 """
7 {'Paul', 'Tom'}
8 {'John'}
9 """

.symmetric_difference()   ^

求交叉补集（就是把各个集合独有的元素都取出来）

 English = ["Lily", "Sally", "Tom", "Paul"]
 Math = ["Lily", "Sally", "John"]
 English_s = set(English)
 Math_s = set(Math)
 print(English_s.symmetric_difference(Math_s))
 """
 {'John', 'Tom', 'Paul'}
 """

集合的类中功能

.add()

　　添加元素

.clear()

　　清空

.copy()

　　拷贝

.pop() .remove(x) .discard(x)

　　第一个任意删除，第二个删除指定的x，若不存在则报错，第三个删除不存在元素不报错

 s = {1,3,5,2,6,5,"sad"}
 s.pop()
 print(s)
 #{2, 3, 5, 6, 'sad'}
 s.remove(5)
 print(s)
 #{2, 3, 6, 'sad'}
 s.discard("sadddd")
 print(s)

.difference_update()

求完差集后更新

 English = ["Lily", "Sally", "Tom", "Paul"]
 Math = ["Lily", "Sally", "John"]
 English_s = set(English)
 Math_s = set(Math)
 English_s.difference_update(Math_s)
 print(English_s)
 #{'Paul', 'Tom'}

.isdisjoint()

判断两个集合是否没有交集，没有则返回True，有则返回False

 s1 = {1,2,3}
 s2 = {2,3,4}
 print(s1.isdisjoint(s2))
 #False

s1.issubset(s2)

判断s1是否是s2的子集

 s1 = {1,2,3}
 s2 = {2,3}
 print(s2.issubset(s1))
 #True

s1.issuperset(s2)

判断s1是否是s2的父集

 s1 = {1,2,3}
 s2 = {2,3}
 print(s1.issuperset(s2))
 #True

s1.update(s2)

将s1更新为s2

 s1 = {1,2,3}
 s2 = {2,3}
 s1.update(s2)
 print(s1)
 #{1, 2, 3}

.add()

与update区别在于该功能只能添加一个值，而update不限

 s1 = {1,2,3}
 s1.add(5)
 print(s1)
 #{1, 2, 3, 5}

 s1 = {1,2,3}
 s1.update({5,6})
 print(s1)
 #{1, 2, 3, 5, 6}

字符串格式化

%s

 msg = "I am %s and I like eating"%"Jenny"  #%是固定格式，s代表是字符串形式
 print(msg)
 #I am Jenny and I like eating
 info = "I am %s and I like %s" %("Kit", "dancing")
 print(info)
 #I am Kit and I like dancing

注意：虽然是%s，但其实可以接受任何类型

　　　但是使用%d，只能接受数字类型

%(key)s

可以使用key的形式来拼接值

%.xf

打印x位浮点数

 perct = 95.76778978757875378538
 msg = "the percent is %.2f"%perct
 print(msg)
 #the percent is 95.77

%.xf  %%

打印百分比

 perct = 95.76778978757875378538
 msg = "the percent is %.2f %%"%perct
 print(msg)
 #the percent is 95.77 %

.format() 格式化

空的{}来传值，不一一对应则报错

{0}，{1}，{2}...可以打乱顺序重新对应

字典形式

可以用字典形式传值，前面加**

可以用元组形式传值，前面加*

 s1 = "I am {}, I hate {}".format("Kit","sleeping")
 print(s1)
 #I am Kit, I hate sleeping
 s2 = "I am {0}, I like{2}  but hate {1}".format("Kit","sleeping","eating")
 print(s2)
 #I am Kit, I likeeating  but hate sleeping
 s3 = "I am {name}, I like {hobby}, but hate {fruit}".format(name="Kit",hobby="music",fruit="banana")
 print(s3)
 #I am Kit, I like music, but hate banana
 s4 = "I am {name}, I like {hobby}, but hate {fruit}".format(**{"name":"Kit","hobby":"music","fruit":"banana"})
 print(s4)
 #I am Kit, I like music, but hate banana
 s5 = "I am {}, I like {}, but hate {}".format(*("Kit","music","banana"))
 print(s5)
 #I am Kit, I like music, but hate banana
 s6 = "I am {:s}, my age is {:d}, and my score is {:%}".format(*("Kit",18,0.15))
 print(s6)
 #I am Kit, my age is 18, and my score is 15.000000%