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%