day 7 - 1 集合、copy及基础数据类型汇总

集合：{}，可变的数据类型，他里面的元素必须是不可变的数据类型，无序，不重复。（不重要）
集合的书写

set1 = set({1,2,3})
#set2 = {1,2,3,[2,3],{'name':'alex'}}  #错的
print(set1)
#print(set2)

set = {'alex','wusir','ritian','egon','barry'}

增 add update

set.add("女神")
print(set)

set.add("abc")
print(set)

set.update("abc")
print(set)

删 pop remove clear del

set.pop()    #随机删除
print(set.pop())
print(set)

set.remove('alex')  #按元素删除
print(set)

set.remove('alex2')
print(set)

set.clear()  #清空列表  set()
print(set)

del set       #删除字典
print(set)

查 for

for i in set:
    print(i)

交集  & intersection

set1 = {1,2,3,4,5}
set2 = {4,5,6,7,8}

set3 = set1 & set2
print(set3)  # {4, 5}
print(set1.intersection(set2))  # {4, 5}

并集  | union

set1 = {1,2,3,4,5}
set2 = {4,5,6,7,8}
print(set1 | set2)  # {1, 2, 3, 4, 5, 6, 7,8}
print(set2.union(set1))  # {1, 2, 3, 4, 5, 6, 7}

反交集 ^ symmetric_difference

set1 = {1,2,3,4,5}
set2 = {4,5,6,7,8}
print(set1 ^ set2)  # {1, 2, 3, 6, 7, 8}
print(set1.symmetric_difference(set2))  # {1, 2, 3, 6, 7, 8}

差集  - difference

set1 = {1,2,3,4,5}
set2 = {4,5,6,7,8}
print(set1 - set2)  # {1, 2, 3}  set1独有的
print(set2 - set1)
print(set1.difference(set2))  # {1, 2, 3}

子集 < issubset
超集 > issuperset

set1 = {1,2,3,}
set2 = {1,2,3,4,5,6}

print(set1 < set2)
print(set1.issubset(set2))  # 这两个相同，都是说明set1是set2子集。

print(set2 > set1)
print(set2.issuperset(set1))  # 这两个相同，都是说明set2是set1超集。

面试题

#去重
li = [1,2,33,33,2,1,4,5,6,6]

set1 = set(li)
print(set1)

li = list(set1)
print(li)

让集合变为不可变类型 frozenset 冻结

s1 = {1,2,3}
print(s1,type(s1))

#让集合变为不可变类型 frozenset 冻结
s = frozenset('barry')
print(s,type(s))

#不可变类型只可以查
for i in s:
    print(i)

 

copy

赋值运算 

l1 = [1,2,3]
l2 = l1
l1.append('a')
print(l1,l2)

[1, 2, 3, 'a'] [1, 2, 3, 'a']

 

运用 copy 赋值

l1 = [1,2,3]
l2 = l1.copy()
print(l1,l2)
print(id(l1),id(l2))
l2.append('a')
print(l1,l2)

 

copy 赋值与数组

#第一组
l1 = [1,2,[4,5,6],3]
l2 = l1.copy()
print(l1,id(l1))
print(l2,id(l2))

#第二组
l1.append('a')
print(l1,l2)

#第三组
l1[2].append('a')
print(l1,l2)
print(id(l1[2]))
print(id(l2[2]))

#第一组
[1, 2, [4, 5, 6], 3] 2371695834312
[1, 2, [4, 5, 6], 3] 2371695834440

#第二组
[1, 2, [4, 5, 6], 3, 'a'] [1, 2, [4, 5, 6], 3]

#第三组
[1, 2, [4, 5, 6, 'a'], 3, 'a'] [1, 2, [4, 5, 6, 'a'], 3]
2371695834184
2371695834184

copy 赋值与数组（2）

l1 = [1,[1],2,3,4]
l2 = l1[:]

#第一组
l1[1].append('a')
#l2 的结果是什么?
print(l2)

#第二组
print(l1,id(l1))
print(l2,id(l2))
print(l1[1] is l2[1])

#第一组
[1, [1, 'a'], 2, 3, 4]

#第二组
[1, [1], 2, 3, 4] 2179834995912
[1, [1], 2, 3, 4] 2179834996040
True

通过定义 copy 赋值

import copy   #定义 copy
l1 = [1,2,[4,5,6],3]
l2 = copys.deepcopy(l1)

#第一组
print(l1,id(l1))
print(l2,id(l2))

#第二组
l1[2].append('a')
print(l1,l2)

#第一组
[1, 2, [4, 5, 6], 3] 1651493850184
[1, 2, [4, 5, 6], 3] 1651493850696

#第二组
[1, 2, [4, 5, 6, 'a'], 3] [1, 2, [4, 5, 6], 3]

 

index 与 enumerate 用法

打印序号与值

li = ['alex','taibai','wusir','egon']
for i in li:
    print(li.index(i),i)

for index,i in enumerate(li,1):
    print(index,i)

 

基础数据类型汇总

list

列表中元素的删除过程
当每次列表中有元素被删除，则列表的原始下标发生变化
range 的值并不会跟随列表的变化而变化

lis = [11,22,33,44,55]
for i in range(len(lis)):
    print(i)       # i = 0              i = 1               i = 2
    del lis[i]
    print(lis)  　　#  [11,22,33,44,55]   [22, 44, 55]          [22, 44]

0
[22, 33, 44, 55]
1
[22, 44, 55]
2
[22, 44]
3
Traceback (most recent call last):
  File "E:/py/day7-1.py", line 4, in <module>
    del lis[i]
IndexError: list assignment index out of range

删除数组中的奇数位

lis = [11,22,33,44,55]

#方法一
lis = lis[::2]
print(lis)

#方法二
l1 = []
for i in lis:
    if lis.index(i) % 2 == 0:
        l1.append(i)
lis = l1
print(lis)

#方法三
for i in range(len(lis)-1,-1,-1):
    if i % 2 == 1:
        print(i)
        del lis[i]
        print(lis)
print(lis)

字典的灵活用法

dic = dict.fromkeys([1,2,3],'春哥')
print(dic)
dic = dict.fromkeys([1,2,3],[])
#dic = dict.fromkeys([1,2,3],['ysg'])
print(dic)  # {1: [], 2: [], 3: []}
dic[1].append('袁姐')
print(dic)
dic[2].extend('二哥')
print(dic)

数组的灵活用法

l1 = []
l2 = l1
l3 = l1
l3.append('a')
print(l1,l2,l3)

不打印含有 k 的键值对

dic = {'k1':'v1','k2':'v2','a3':'v3'}

#方法一：字典
dic1 = {}
for i in dic:
    if 'k' not in i:
        dic1.setdefault(i,dic[i])
dic = dic1
print(dic)

#方法二：数组
l = []
for i in dic:
    if 'k' in i:
        l.append(i)
for i in l:
    del dic[i]
print(dic)

可以转化成 bool 值

0 ''  [] () {} set()

元祖：如果元祖里面只有一个元素且不加逗号，那此元素是什么类型，该元祖就是什么类型。

#第一组
tu1 = (1)
tu2 = (1,)
print(tu1,type(tu1))
print(tu2,type(tu2))

#第二组
tu1 = ([1])
tu2 = ([1],)
print(tu1,type(tu1))
print(tu2,type(tu2))

#元祖的灵活用法
dic = dict.fromkeys([1,2,3,],3)
dic[1] = 4
print(dic)

#第一组
1 <class 'int'>
(1,) <class 'tuple'>

#第二组
[1] <class 'list'>
([1],) <class 'tuple'>

#元祖的灵活用法
{1: 4, 2: 3, 3: 3}