Set: {}, variable data type. The elements in it must be immutable data type, unordered and not repeated. (unimportant)
The writing of set

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

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

add update

set.add("goddess")
print(set)

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

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

Delete pop remove clear set

 

set.pop()  #Random deletion
print(set.pop())
print(set)

set.remove('alex')  #Delete by element
print(set)

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

set.clear()  #clear list  set()
print(set)

 

Check for

 

for i in set:
    print(i)

 

Intersection & 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}

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}

Reciprocal 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}

Difference - difference

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

Subset < issubset
Superset > issuperset

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

print(set1 < set2)
print(set1.issubset(set2))  # The two are the same set1 yes set2 Subset.

print(set2 > set1)
print(set2.issuperset(set1))  # The two are the same set2 yes set1 Superset.

Interview questions

#Duplicate removal
li = [1,2,33,33,2,1,4,5,6,6]

set1 = set(li)
print(set1)

li = list(set1)
print(li)

Make the set immutable type freeze

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

#Make a set immutable   frozenset Frozen
s = frozenset('barry')
print(s,type(s))

#Immutable type can only be checked
for i in s:
    print(i)

copy

Assignment operation

 

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

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

 

Using copy assignment

 

 

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

 

copy assignment and array

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

#Second group
l1.append('a')
print(l1,l2)

#Third group
l1[2].append('a')
print(l1,l2)
print(id(l1[2]))
print(id(l2[2]))

#first group
[1, 2, [4, 5, 6], 3] 2371695834312
[1, 2, [4, 5, 6], 3] 2371695834440

#Second group
[1, 2, [4, 5, 6], 3, 'a'] [1, 2, [4, 5, 6], 3]

#Third group
[1, 2, [4, 5, 6, 'a'], 3, 'a'] [1, 2, [4, 5, 6, 'a'], 3]
2371695834184
2371695834184

copy assignment and array (2)

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

#first group
l1[1].append('a')
#l2 What is the result of?
print(l2)

#Second group
print(l1,id(l1))
print(l2,id(l2))
print(l1[1] is l2[1])

#first group
[1, [1, 'a'], 2, 3, 4]

#Second group
[1, [1], 2, 3, 4] 2179834995912
[1, [1], 2, 3, 4] 2179834996040
True

Assign by defining copy

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

#first group
print(l1,id(l1))
print(l2,id(l2))

#Second group
l1[2].append('a')
print(l1,l2)

#first group
[1, 2, [4, 5, 6], 3] 1651493850184
[1, 2, [4, 5, 6], 3] 1651493850696

#Second group
[1, 2, [4, 5, 6, 'a'], 3] [1, 2, [4, 5, 6], 3]

index and enumerate usage

Print sequence number and value

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

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

Basic data type summary

list

Deletion process of elements in the list
Each time an element in the list is deleted, the original subscript of the list changes
The value of range does not change as the list changes

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

Delete odd digits in an array

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

#Method 1
lis = lis[::2]
print(lis)

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

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

Flexible use of dictionaries

dic = dict.fromkeys([1,2,3],'Spring elder brother')
print(dic)
dic = dict.fromkeys([1,2,3],[])
#dic = dict.fromkeys([1,2,3],['ysg'])
print(dic)  # {1: [], 2: [], 3: []}
dic[1].append('Yuan Jie')
print(dic)
dic[2].extend('Second elder brother')
print(dic)

Flexible use of arrays

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

Do not print key value pairs with k

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

#Method 1: Dictionary
dic1 = {}
for i in dic:
    if 'k' not in i:
        dic1.setdefault(i,dic[i])
dic = dic1
print(dic)

#Method 2: array
l = []
for i in dic:
    if 'k' in i:
        l.append(i)
for i in l:
    del dic[i]
print(dic)

Can be converted to bool value

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

Yuanzu: if there is only one element in Yuanzu without comma, then what type is this element and what type is the Yuanzu.

#first group
tu1 = (1)
tu2 = (1,)
print(tu1,type(tu1))
print(tu2,type(tu2))

#Second group
tu1 = ([1])
tu2 = ([1],)
print(tu1,type(tu1))
print(tu2,type(tu2))

#The flexible usage of Yuan Zu
dic = dict.fromkeys([1,2,3,],3)
dic[1] = 4
print(dic)

#first group
1 <class 'int'>
(1,) <class 'tuple'>

#Second group
[1] <class 'list'>
([1],) <class 'tuple'>

#The flexible usage of Yuan Zu
{1: 4, 2: 3, 3: 3}