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

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%

巴特西

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：

2、访问顺序：

3、存放元素个数：

集合

注意：另一种定义方式可以将集合定义为不可变类型

集合的运算关系

.intersection() &

.union() |

.difference() -

.symmetric_difference() ^

集合的类中功能

.add()

.clear()

.copy()

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

.difference_update()

.isdisjoint()

s1.issubset(s2)

s1.issuperset(s2)

s1.update(s2)

.add()

字符串格式化

%s

%(key)s

%.xf

%.xf %%

.format() 格式化

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