Python 核心编程
- [1. 数据类型](#1. 数据类型)
-
- [1.1 整型 int](#1.1 整型 int)
- [1.2 浮点数 float](#1.2 浮点数 float)
- [1.3 布尔类型 bool](#1.3 布尔类型 bool)
- [1.4 字符串 str](#1.4 字符串 str)
- [1.5 列表 list](#1.5 列表 list)
- [1.6 元组 tuple](#1.6 元组 tuple)
- [1.7 集合 set](#1.7 集合 set)
- [1.8 字典 dict](#1.8 字典 dict)
- [2. 逻辑结构、文件操作](#2. 逻辑结构、文件操作)
-
- [2.1 分支结构和三元表达](#2.1 分支结构和三元表达)
- [2.2 循环和遍历](#2.2 循环和遍历)
- [2.3 目录和路径](#2.3 目录和路径)
- [2.4 文件操作](#2.4 文件操作)
- [3. 函数、类、异常处理](#3. 函数、类、异常处理)
-
- [3.1 函数](#3.1 函数)
- [3.2 类](#3.2 类)
- [3.3 异常处理](#3.3 异常处理)
- [4. 包和模块、随机数](#4. 包和模块、随机数)
-
- [4.1 包和模块](#4.1 包和模块)
- [4.2 随机数](#4.2 随机数)
- [5. 生成器、高阶函数](#5. 生成器、高阶函数)
1. 数据类型
1.1 整型 int
- 没有长度限制
python
score = 95
python
type(score)int
python
num = 888888888888888888888888888888888888888888888888888888888888888888888888888888
python
type(num)int
python
num888888888888888888888888888888888888888888888888888888888888888888888888888888
python
a = 4
b = 3
python
a + b7
python
a - b1
python
a * b12
python
a / b1.3333333333333333
python
a ** b64
python
a ** (1 / b)1.5874010519681994
python
import math
python
math.exp(3)20.085536923187668
python
math.log(a)1.3862943611198906
python
str(a)'4'
python
c = int('5')
python
c5
python
a > bTrue
python
b > aFalse
python
a == bFalse
python
a >= bTrue
python
a <= bFalse
python
a != bTrue1.2 浮点数 float
- 浮点数是不精准存储
python
score = 82.11
python
type(score)float
python
price = 5.55555555555555555555555555555555555555555555555555555555555
python
price5.555555555555555
python
type(price)float
python
distance = 1.5e-4
python
distance0.00015
python
a = 1.5
b = 2.7
python
a + b4.2
python
a - b-1.2000000000000002
python
a * b4.050000000000001
python
a / b0.5555555555555555
python
import math
python
a = 3.5
python
a ** 212.25
python
a ** (1/2)1.8708286933869707
python
a = 5.6
python
math.exp(a)270.42640742615254
python
math.log(a)1.7227665977411035
python
math.log2(a)2.4854268271702415
python
str(a)'5.6'
python
c = float('2.3132')
python
c2.3132
python
a = 3.23452
python
math.ceil(a)4
python
math.floor(a)3
python
int(a)3
python
round(a,2)3.23
python
a = 1-0.55
python
a0.44999999999999996
python
a = 3.5
b = 6.43
python
a < bTrue
python
a = 1 - 0.55
python
a == 0.45False
python
# 浮点数的相等不能直接比较
math.fabs(a - 0.45) < 1e-6True1.3 布尔类型 bool
- True 就是1 ， False 就是0
python
TrueTrue
python
FalseFalse
python
result = True
python
3>2True
python
1==2False
python
True+12
python
2 ** True2
python
1 / False---------------------------------------------------------------------------
ZeroDivisionError Traceback (most recent call last)
Cell In[85], line 1
----> 1 1 / False
ZeroDivisionError: division by zero
python
True and TrueTrue
python
True and FalseFalse
python
True or FalseTrue
python
not FalseTrue
python
not TrueFalse1.4 字符串 str
- 单引号/双引号/三单引号/三双引号
python
s1 = '人工智能'
s2 = "人工智能"
python
type(s1),type(s2)(str, str)
python
s3='''这是一个多行字符串
我可以自由换行
'''
python
s3'这是一个多行字符串\n我可以自由换行\n'
python
s4="""三双引号
一样可以灵活换行"""
python
s4'三双引号\n一样可以灵活换行'
python
len(s4)13
python
s4.__len__()13
python
s="qwertyuiopezxcfvgbnhmpdsfkpisjfoid"
python
s[0]'q'
python
s[10]'e'
python
s[-1]'d'
python
s[-2]'i'
python
s[:3]'qwe'
python
s[3:5]'rt'
python
s[1:-1]'wertyuiopezxcfvgbnhmpdsfkpisjfoi'
python
len(s)34
python
#[start:stop:step]
s[1:-4:3]'wtiecghdks'
python
for ele in s[5:-6:4]:
print(ele)y
p
c
b
p
k
python
s = " erwreqw"
python
s.strip()'erwreqw'
python
s = " \t\n AI \t \n"
python
s' \t\n AI \t \n'
python
s.strip()'AI'
python
s = "人工 \t智能"
python
s.strip()'人工 \t智能'
python
s.replace("\t","").replace(" ","")'人工智能'
python
s = "1,2,3,4,5,6 "
python
ls = s.strip().split(",")
python
ls['1', '2', '3', '4', '5', '6']
python
s = ",".join(ls)
python
s'1,2,3,4,5,6'
python
s = "Hello World"
python
s.lower()'hello world'
python
s.upper()'HELLO WORLD'
python
s1 = "AI "
s2 = "人工智能 "
python
s1+s2'AI 人工智能 '
python
s = 3*s1+ 5* s2
python
s'AI AI AI 人工智能 人工智能 人工智能 人工智能 人工智能 '
python
s.count("AI")3
python
'人工' in sTrue
python
'智能' not in sFalse1.5 列表 list
- 元素有顺序，元素可以是任意类型，元素可以重复
python
ls = [1,2,3,4]
python
type(ls)list
python
ls = list("abc")
python
ls['a', 'b', 'c']
python
[1,2] == [2,1]False
python
ls = [1,True,"asd",[1,2,3,4]]
python
ls[1, True, 'asd', [1, 2, 3, 4]]
python
len(ls)4
python
ls.__len__()4
python
ls[0]1
python
ls[:2][1, True]
python
ls[::2][1, 'asd']
python
ls[::-1][[1, 2, 3, 4], 'asd', True, 1]
python
for ele in ls:
print(ele)1
True
asd
[1, 2, 3, 4]
python
ls=[]
python
len(ls)0
python
ls.insert(0,"test")
python
ls['test']
python
ls.insert(0,"1")
python
ls['1', 'test']
python
ls.insert(100,"2")
python
ls['1', 'test', '2']
python
ls.insert(-100,123)
python
ls[123, '1', 'test', '2']
python
ls.append([1,2,3])
python
ls[123, '1', 'test', '2', [1, 2, 3]]
python
ls.extend("mech")
python
ls[123, '1', 'test', '2', [1, 2, 3], 'm', 'e', 'c', 'h']
python
ls.remove("1")
python
ls.remove([1,2,3])
python
ls[123, 'test', '2', 'm', 'e', 'c', 'h']
python
ls.remove(321)---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
Cell In[217], line 1
----> 1 ls.remove(321)
ValueError: list.remove(x): x not in list
python
ls.pop()'h'
python
ls[123, 'test', '2', 'm', 'e', 'c']
python
ls.pop(10)---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
Cell In[220], line 1
----> 1 ls.pop(10)
IndexError: pop index out of range
python
ls.pop(-3)'m'
python
ls[123, 'test', '2', 'e', 'c']
python
ls[0] = 321
python
ls[321, 'test', '2', 'e', 'c']
python
ls[-3:] = [1.1,2.2]
python
ls[321, 'test', 1.1, 2.2]
python
ls.count(1)0
python
321 in lsTrue1.6 元组 tuple
- 元素有顺序，可以是任意类型，不可修改
python
t1 = ()
python
type(t1)tuple
python
t1()
python
t2 = ("qwe")
python
t2'qwe'
python
type(t2)str
python
t3 = ("12",)
python
t3('12',)
python
type(t3)tuple
python
t4=(1,2,True,"ADSAS")
python
t4(1, 2, True, 'ADSAS')
python
t5 = tuple("abd")
python
t5('a', 'b', 'd')
python
t6=tuple([1,2,3,4,5,6])
python
t6(1, 2, 3, 4, 5, 6)
python
# 元素不能修改
t6[3]=0---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In[248], line 2
1 # 元素不能修改
----> 2 t6[3]=0
TypeError: 'tuple' object does not support item assignment
python
t1 = tuple("abc")
python
t1('a', 'b', 'c')
python
len(t1)3
python
t1.__len__()3
python
t1[0]'a'
python
t1[-1]'c'
python
t1[1::-1]('b', 'a')
python
# 省略括号和结构赋值
t1 = (1,4.3)
python
t2 = 1,4.3
python
t1==t2True
python
p1,p2 = t2
python
p1,p2(1, 4.3)
python
p11
python
p24.3
python
p1,p2,p3 = t2---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
Cell In[265], line 1
----> 1 p1,p2,p3 = t2
ValueError: not enough values to unpack (expected 3, got 2)
python
# 快速交换多个变量的值
A = 4
B = 5
python
A,B=B,A
python
A5
python
B4
python
ls = (1,2,3,True,1,3,4,2,12)
python
ls.count(1)3
python
ls.count(True)3
python
True in lsTrue
python
False in lsFalse
python
# tuple 元素不能修改吗？
t2 = (1,2,3)
python
t2[1]=3---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In[279], line 1
----> 1 t2[1]=3
TypeError: 'tuple' object does not support item assignment
python
t3=(1,2,[4,5,6])
python
# 列表是可变元素，值变了，但地址没变
t3[-1].append("ABD")
python
t3(1, 2, [4, 5, 6, 'ABD'])1.7 集合 set
- 元素的无序性/确定性/唯一性
python
s1 = {}
python
s1{}
python
type(s1)dict
python
t2 = set()
python
t2set()
python
type(t2)set
python
t3={1}
python
t3{1}
python
t4={1,2,3,4,5,6,7}
python
t4{1, 2, 3, 4, 5, 6, 7}
python
t5=set("abscs")
python
t5{'a', 'b', 'c', 's'}
python
t6=set([1,2,3,4])
python
t6{1, 2, 3, 4}
python
t7 = {1,1,1,1,2,3,4}
python
t7{1, 2, 3, 4}
python
# 列表是可变的，不能作为集合的元素
t8 = {[1,2,3],True,"absd"}---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In[301], line 2
1 # 列表是可变的，不能作为集合的元素
----> 2 t8 = {[1,2,3],True,"absd"}
TypeError: unhashable type: 'list'
python
s = set("asdfdwsf")
python
len(s)5
python
s.__len__()5
python
s.add(True)
python
s{True, 'a', 'd', 'f', 's', 'w'}
python
s.add('s')
python
s{True, 'a', 'd', 'f', 's', 'w'}
python
s.remove('a')
python
s{True, 'd', 'f', 's', 'w'}
python
s.remove('ffff')---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
Cell In[313], line 1
----> 1 s.remove('ffff')
KeyError: 'ffff'
python
# 随机删除
s.pop()'d'
python
s{'s', 'w'}
python
a = {1,2,3,4,5,6,7}
b = {4,5,6,7,8,9}
python
a.intersection(b){4, 5, 6, 7}
python
b.intersection(a){4, 5, 6, 7}
python
a.union(b){1, 2, 3, 4, 5, 6, 7, 8, 9}
python
b.union(a){1, 2, 3, 4, 5, 6, 7, 8, 9}
python
1 in aTrue
python
10 in bFalse1.8 字典 dict
- 元素成对出现，元素五顺序，key不可变，不重复，value无要求
python
d1 = {}
python
d1{}
python
type(d1)dict
python
len(d1)0
python
d2 = {"name":"Tom"}
python
d2{'name': 'Tom'}
python
d3 = {'name': 'Tom','age':12}
python
d3{'name': 'Tom', 'age': 12}
python
len(d3)2
python
# 可变类型不可以做key
# 可变类型： list/set/dict
# 不可变类型： int/float/bool/str/tuple*
d4 = {[1,2,3]:12}---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In[339], line 2
1 # 可变类型不可以做key
----> 2 d4 = {[1,2,3]:12}
TypeError: unhashable type: 'list'
python
d5 = dict(a=1,b=2,c=3)
python
d5{'a': 1, 'b': 2, 'c': 3}
python
len(d5)3
python
d5.__len__()3
python
d6 = dict(name='Tom',age=22,school='北京大学')
python
d6{'name': 'Tom', 'age': 22, 'school': '北京大学'}
python
d6["score"]=87
python
d6{'name': 'Tom', 'age': 22, 'school': '北京大学', 'score': 87}
python
# 有则改之，无则追加
d2["score"] = 98
python
d2{'name': 'Tom', 'score': 98}
python
d2["score"]98
python
# 读取不存在的key会报错
d["asd"]---------------------------------------------------------------------------
NameError Traceback (most recent call last)
Cell In[364], line 2
1 # 读取不存在的key会报错
----> 2 d["asd"]
NameError: name 'd' is not defined
python
# 使用get读取更加安全
d6.get("abc",0)0
python
d6{'name': 'Tom', 'age': 22, 'school': '北京大学', 'score': 87}
python
d6.pop('name')'Tom'
python
d6{'age': 22, 'school': '北京大学', 'score': 87}
python
d.pop('age1')---------------------------------------------------------------------------
NameError Traceback (most recent call last)
Cell In[371], line 1
----> 1 d.pop('age1')
NameError: name 'd' is not defined
python
d6.keys()dict_keys(['age', 'school', 'score'])
python
d6.values()dict_values([22, '北京大学', 87])
python
d6.items()dict_items([('age', 22), ('school', '北京大学'), ('score', 87)])
python
# 默认遍历key
for ele in d2:
print(ele)name
score
python
# 遍历key
for key in d6.keys():
print(key)age
school
score
python
# 遍历value
for value in d6.values():
print(value)22
北京大学
87
python
# 遍历键值对
for key,value in d6.items():
print(key,value)age 22
school 北京大学
score 87
python
'age' in d6True
python
'age1' in d6False2. 逻辑结构、文件操作
2.1 分支结构和三元表达
python
if(1<2):
print("1<2")1<2
python
age = 25
if age >= 18:
print("成年人")
else:
print("未成年")成年人
python
score= 89
if score >=90:
print("优秀")
elif score >= 75:
print("良好")
elif score >= 60:
print("及格")
else:
print("不及格")良好
python
# 三元表达
age = 3
True if age >= 18 else FalseFalse
python
"成年人" if age >=18 else "未成年"'未成年'
python
"成年人" if age >=18 else age32.2 循环和遍历
python
num = 1
while True:
if num < 10:
num+=1
print(num)
else:
break2
3
4
5
6
7
8
9
10
python
for _ in range(10):
print("Hello,Python!!!")Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
Hello,Python!!!
python
ls = [1,2,3,4,5,"Hello",False]
for ele in ls:
print(ele)1
2
3
4
5
Hello
False
python
s = "asdfg"
for ele in s:
print(ele)a
s
d
f
g2.3 目录和路径
python
import os
python
# 路径是否存在(文件夹或文件)
os.path.exists(path="./abc")True
python
# 路径拼接
os.path.join(".","abc","ddd")'.\\abc\\ddd'
python
# 创建目录
save_path = "./abc/saved_weight"
# 如果不存在就创建
if not os.path.exists(path=save_path):
os.makedirs(save_path)
python
# 删除文件
if os.path.exists(path="ddd.ddd"):
os.remove()
python
# 删除目录
save_path = "./abc/saves_weights"
if os.path.exists(path=save_path):
print("存在")
os.removedirs(name=save_path)
python
# 遍历一个目录
root = "./"
for ele in os.listdir(root):
if os.path.isfile(ele):
print(ele,"文件")
elif os.path.isdir(ele):
print(ele,"目录").ipynb_checkpoints 目录
12.csv 文件
1234.txt 文件
abc 目录
P1_数据类型.ipynb 文件
P2_逻辑结构及文件操作.ipynb 文件
poem.txt 文件
saved_weight 目录2.4 文件操作
python
# 打开、增删改查、关闭
python
f = open(file="./1234.txt",mode="r",encoding="utf8")
python
f.read()'锄禾日当午\n汗滴禾下土'
python
f.read()''
python
f.close()
python
# 更加优雅的写法
with open(file="./1234.txt",mode="r",encoding="utf8") as f:
while True:
line = f.readline().strip()
if line:
print(line)
else:
break锄禾日当午
汗滴禾下土
python
# 写入：如果文件不存在则新建，如果存在则清空文件内容
with open(file="poem.txt",mode="w",encoding="utf8") as f:
f.write("举头望明月\n低头思故乡\n")
python
# 追加内容
with open(file="poem.txt",mode="a",encoding="utf8") as f:
f.write("举头望明月\n低头思故乡\n")3. 函数、类、异常处理
3.1 函数
- 位置参数
- 默认参数
- 可变参数
- 匿名函数
python
# 定义参数
def fun():
pass
python
# 调用
fun()
python
callable(fun)True
python
# 位置参数
def add(a,b):
return a+b
python
add(1,2)3
python
# 默认参数
def area(r,pi=3.1415926):
return r*r*pi
python
area(r=3,pi=3.14)28.26
python
# 可变参数
def add_num(*args):
s = 0
for ele in args:
s += ele
return s
python
add_num()0
python
add_num(1)1
python
add_num(1,2,3,4,5)15
python
# 匿名函数
fn = lambda x: x ** 2
python
fn(3)9
python
(lambda x,y:x+y)(1,2)33.2 类
- 封装
- 继承
- 多态
python
class Car(object):
def __init__(self,color="Black",brand="BYD",price=50):
'''
自定属性
'''
self.color = color
self.brand = brand
self.price = price
def info(self):
'''
自定义方法
'''
print(self.color,self.brand,self.price)
def __repr__(self):
'''
重载父类的方法
'''
return 'Car'
python
car1 = Car(color="Blue")
python
car1Car
python
print(car1.color)Blue
python
car1.info()Blue BYD 50
python
# 继承
car1.__repr__()'Car'
python
o = object()
python
o.__repr__()'<object object at 0x0000020EBEBE4ED0>'
python
# 多态
car1.__repr__()'Car'3.3 异常处理
- 异常基类 Exception
- 接收异常 try except else finally
- 抛出异常 raise
python
def divide(a, b):
return a / b
python
divide(1,2)0.5
python
divide(2,0)---------------------------------------------------------------------------
ZeroDivisionError Traceback (most recent call last)
Cell In[13], line 1
----> 1 divide(2,0)
Cell In[11], line 2, in divide(a, b)
1 def divide(a, b):
----> 2 return a / b
ZeroDivisionError: division by zero
python
"""
异常处理
- 守株待兔的操作
- 如果没有发生异常：不做任何额外处理
- 如果发生了异常，引导程序做出合理化的处理
"""
a = 3
b = 0
try:
result = divide(a,b)
print(result)
except Exception as e:
print(e)
else:
print("没有发生错误")
finally:
print("不管是否发生错误，我都会执行")
print("这里依然可以执行")division by zero
不管是否发生错误，我都会执行
这里依然可以执行
python
# 抛出异常
a = 2
b = 3
def divide(a, b):
if isinstance(a, int) and isinstance(b, int) and b != 0:
return a / b
else:
raise Exception("参数错误")
python
divide(2,1)2.0
python
divide(1,0.3)---------------------------------------------------------------------------
Exception Traceback (most recent call last)
Cell In[23], line 1
----> 1 divide(1,0.3)
Cell In[21], line 10, in divide(a, b)
8 return a / b
9 else:
---> 10 raise Exception("参数错误")
Exception: 参数错误4. 包和模块、随机数
4.1 包和模块
- 包和模块是代码组织的一种方式，包就是一个文件夹，模块就是一个源码文件
- 避免重复造轮子，利用前人写好的包和模块
- 托管平台：pip 和 conda 管理工具
python
import numpy as np
python
np.__version__'1.23.5'
python
np.e2.718281828459045
python
import os
python
os.path.exists("./")True
python
from matplotlib import pyplot as plt- 定义自己的模块
- 在项目文件夹中新建一个文件夹名为 utils ,在里面新建一个 math.py文件，然后编辑函数
python
from utils import math
python
math.add(3,23)26
python
math.sub(43,1)424.2 随机数
- 概率论中随机试验产生的结果
- 数据科学中随机数很重要
python
import random
python
# 均匀分布
# 按照均匀分布生成一个随机数
random.uniform(0,100)4.646385375119754
python
random.randint(0,100)67
python
# 高斯分布
random.gauss(mu=0,sigma=1)-2.9510713969400872
python
# 洗牌操作
x = [1,2,3,4,5,6,7,8,9,0]
print(x)
random.shuffle(x)
print(x)[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
[0, 6, 1, 4, 5, 7, 3, 9, 8, 2]
python
# 随机抽取
x = [1,2,3,4,5,6,7,8,9,0]
result = random.choice(x)
print(result)9
python
ls = random.sample(x,3)
print(ls)[5, 9, 3]
python
# 固定随机数，方便复现：种子固定了，随机规则就产生了，
random.seed(0)
x = [1,2,3,4,5,6,7,8,9,0]
result = random.sample(x,2)
print(result)[7, 0]5. 生成器、高阶函数
生成器
- 当数据集很大时，我们很难一次性将所有数据加载到内存中，而是按需加载，这时候就要用到生成器
- 模型训练时，数据经常会打包成生成器
- yield 和 return
- 列表生成器
- 打包数据集
python
# return 返回并跳出函数
def get_data():
ls = [0,1,2,3,4,5,6,7,8,9]
for ele in ls:
return ele
python
get_data()0
python
# yield 构建生成器
def get_data():
ls = [0,1,2,3,4,5,6,7,8,9]
for ele in ls:
yield ele
python
gen = get_data()
python
for ele in gen:
print(ele)0
1
2
3
4
5
6
7
8
9
python
ls = list(range(10))
python
ls[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
python
# 列表解析式 ： for循环 + if判断
ls1 = [ele for ele in ls if ele % 2 == 1]
python
ls1[1, 3, 5, 7, 9]
python
# 这样也可以构建生成器
gen1 = (ele for ele in ls if ele % 2 == 1)
python
for ele in gen1:
print (ele)1
3
5
7
9
python
# 通过生成器来读取数据集
def get_dataset():
with open(file="dataset.csv",mode="r",encoding="utf8") as f:
line = f.readline()
while True:
line = f.readline()
if line:
yield line
else:
break
python
gen = get_dataset()
python
# 生成器是一次性的，从头读到尾之后，再想重新读就又要新的生成器了
next(gen)'1.70,70,23,89\n'
python
for ele in gen:
print(ele)1.67,71,23,79
1.75,72,22,84
1.74,73,23,86
1.79,74,21,56高阶函数
- 把函数当做参数，自动化的实现底层遍历
- 数据科学中高阶函数很有用，可以极大提升效率
- map 映射
- reduce 聚合
- filter 过滤
- sorted 排序- map
python
ls = [0,1,2,3,4,5,6,7,8,9]
def add(ele):
return ele + 0.5
python
ls1 = list(map(add,ls))
python
ls1[0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5]- reduce
python
from functools import reduce
python
sum(ls)45
python
def add(a,b):
return a+b
python
reduce(add,ls)45
python
reduce(lambda x, y: x * y, ls)0- filter
python
list(filter(lambda x : True if x % 2 == 0 else False, ls))[0, 2, 4, 6, 8]- sorted
python
sorted(ls, reverse = True)[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
python
ls = [0,1,2,3,4,5,6,7,8,9]
python
ls.sort(reverse = True)
python
ls[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
python
ls2 = [(2,4),(1,6),(5,1),(3,8)]
python
sorted(ls2, key=lambda x:x[0], reverse=True)[(5, 1), (3, 8), (2, 4), (1, 6)]
python
sorted(ls2, key=lambda x:x[1],reverse=False)[(5, 1), (2, 4), (1, 6), (3, 8)]