Some advanced additions to Python

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Refer to "Python3 from entry to actual combat"

1. You can use isinstance() to determine whether an object is a certain type of object

print(isinstance(2,int)) #判断2是int类型的对象吗?
运行结果如下:
True

Second, Python can express the base by prefixing the number:

1. Add 0b or 0B to represent the binary number;

2. Add prefix 0o or 0O to represent octal number;

3.Add prefix 0x or 0X to represent hexadecimal number.

print(0b0110100101)
print(0o703516)
print(0x7F3BA)
运行结果如下：
421
231246
521146

Three: You can use the built-in functions bin(), oct(), and hex() to get the corresponding string of a number in binary, octal, and hexadecimal:

print(bin(412))
print(oct(412))
print(hex(412))
运行结果如下:
0b110011100
0o634
0x19c

Four: Python provides high-precision Decimal class and Fraction class for fraction calculation:

import Decimal
from fractions import Fraction as F
print(0.1)
print(F(1,3))#表示分数1/3
print(1/F(5,6))#表示分数6/5

#Python用于数值计算的函数
print(abs(-3.4))
print(min(3.4,2.8))
print(max(3.4,2.8))
print(pow(0.3,4))
print(round(2.8))#取最接近的整数
print(round(2.3))
print(round(-2,3))
运行结果如下:
3.4
2.8
3.4
0.0081
3
2
-2

Five: Import the math module:

	import math
    print("*"*50)
    print(math.pi)
    print(math.e)
    
    #浮点计算可能产生两个异常值,inf和nan,也可能抛出一个OverflowError异常。
    #当浮点数超过float类型数值表示范围时,产生的结果是无穷大(inf)
    #并不是所有溢出的值都用inf表示,结果是inf还是异常是底层C Python决定的
    
    print("*"*50)
    x = 10.0 ** 200
    y = x*x
    print(y)
    print(math.isinf(y)) 
    
    #如果除inf的结果是未定的，则结果是nan(未定的数值).
    #因为nan不能和其他值进行比较,所以只能用函数ianan()检查nan
    
    print("*"*50)
    x = (10.0) ** 200 * (10.0) ** 200
    y = x/x
    print(y)
    print(math.isnan(y))
    
	运行结果如下:
	**************************************************
	3.141592653589793
	2.718281828459045
	**************************************************
	inf
	True
	**************************************************
	nan
	True

Six: You can also use the function isfinite() to check whether a value is a regular value or a special value inf or nan

import math
for i in [math.pi,math.nan,math.inf]:
	print(math.isfinite(i))
运行结果如下:
True
False
False

Seven: equality comparison of floating-point numbers

1.isclose(a,b,*,rel_tol=le-09,abs_tol=0.0): The default parameters rel_tol and abs_tol represent relative error and absolute error respectively

import math
a = 1.0 - 0.99
b = 100 - 99.99
print(a==b)
print(math.isclose(a, b))
运行结果如下:
False
True

Eight: floating-point number converted to integer

1. The function trunc() truncates the decimal part of a floating-point number

2. The function floor() can be converted to the largest integer smaller than it

3. The function ceil() converts a floating point number to the smallest integer larger than it

import math
a = 1.8
print(math.trunc(a))
print(math.floor(a))
print(math.ceil(a))
运行结果如下
1
1
2

4.sqrt(x) is used to calculate the square root of a number x

5.pow(x,y) is used to calculate the y power of x, similar to x ** y, but pow (x, y) can be guaranteed to operate according to floating point numbers, and x ** y can only return an int or float

6.exp(x) Exponential function with natural constant as the base

7.expml(x) calculate e**x-1

8. The logarithmic function log(x,base) has base and some variants log2(x) log10(x) log1p(x):

from math import *
print(sqrt(9))
print(pow(3,3))
print(exp(1))
print(expm1(1))
print(log10(10))
print(log1p(1))
#什么都不写就是ln
print(log(e))
运行结果如下:
3.0
27.0
2.718281828459045
1.718281828459045
1.0
0.6931471805599453
1.0

Nine: Angles and radians

1. The function radians() converts the angle value into radians

2. The function degrees() converts a radian value into an angle value

from math import *
print(radians(45))
print(degrees(pi))
运行结果如下:
0.7853981633974483
180.0

Ten: The math module contains various trigonometric functions and inverse trigonometric functions such as sin, cos, tan, atan.

from math import *
print(sin(0))
print(cos(0))
print(tan(0))
print(degrees(atan(1)))#转化成角度了

运行结果如下:
0.0
1.0
0.0
45.0

11. Random number: random module

import random
l = [1,2,3,4]
print(random.random())#0-1的随机小数
print(random.randint(100, 900))#100-900的随机数
print(random.choice(l))#任意选取一个列表中的元素
random.shuffle(l)#打乱列表
print(l)

'''
0.9724452742237619
188
1
[1, 2, 4, 3]
'''