啃书 -- 流畅的python 第二章 丰富的序列

colors = ['black', 'white']

sizes = ['S', 'M', 'L']



#列表推导式

tshirts\_list= [f"({color},{size})" for color in colors

                                   for size  in sizes]

#生成器推导式

tshirts\_tuple= (f"({color},{size})" for color in colors

                                    for size  in sizes)

print(tshirts\_list)

#直接打印tshirts\_tuple 

print(tshirts\_tuple)

#遍历打印tuple 

for item in tshirts\_tuple:

    print(item)

#可见生成器不会生成包含6个元素的列表，而是会一个个生成

['(black,S)', '(black,M)', '(black,L)', '(white,S)', '(white,M)', '(white,L)']

<generator object <genexpr> at 0x000001AEE9649F50>

(black,S)
(black,M)
(black,L)
(white,S)
(white,M)
(white,L)

a=(10,'a',[1,2])

b=(10,'a',[1,2]) # 注意到第3项存放的list 是可变项，因此

print(a)

#b[-1] = [2,3]   值的变化error， 因为tuple不支持赋值；

b[-1].append(99) #append 可pass

print(b)

(10, 'a', [1, 2])
(10, 'a', [1, 2, 99])

# 拆包： 

#并行赋值、值调换

a,b = 10,15

b,a = a,b

print(a,b)

#传参

t=(10,20)

quotient,remainder = divmod(*t) # 若去掉* 则报错： 函数需要2个参数但只传了一个参数

print(f"{quotient} {remainder}")

#函数输出

import os

file_path = "C:/Users/AppData/Roaming/Microsoft/Windows/ppt.pptx"

_,file = os.path.split(file_path)

print(file)

#tuple的嵌套拆包

metro\_areas = [('Tokyo', 'JP', 36.933, (35.689722, 139.691667)), 

               ('Delhi NCR', 'IN', 21.935, (28.613889, 77.208889)), 

               ('Mexico City', 'MX', 20.142, (19.433333, -99.133333)),

               ('New York-Newark', 'US', 20.104, (40.808611, -74.020386)),

               ('São Paulo', 'BR', 19.649, (-23.547778, -46.635833)), ]

print(f'{"":15}|{"latitude":>9}|{"longititude":>10}')

for city,_,_,(latitude,longititude) in metro_areas:

    print(f"{city:>15}|{latitude:9.4f}|{longititude:9.4f}")

a,b,*c = range(1,10)

print(a,b,c)

a,*b,c =  range(1,10)

print(a,b,c)

1 2 [3, 4, 5, 6, 7, 8, 9]
1 [2, 3, 4, 5, 6, 7, 8] 9
(1, 2, (3, 4))

def func(a,b,\*c):

    return a,b,c

print(func(\*(1,2),3,4))  # \*用来指示拆包；对不不带\* 会发生什么：

print(func((1,2),3,4))

(1, 2, (3, 4))
((1, 2), 3, (4,))

#序列字面量赋值

#tuple

a,b,c = \*range(2),3 #注意不能去掉,3 否则无法判断是否是tuple ， 拆包出现语法错误

print(a,b,c)

print([\*range(4)])

print(\*range(4),4,5,\*range(6))

0 1 3
[0, 1, 2, 3]
0 1 2 3 4 5 0 1 2 3 4 5

def op(command):

    match command:

        case('mpu',mpu\_operate):

            print(f"mpu {mpu\_operate}")

        case('dma',dma\_op,data\_amount\_Byte):

            print(f"dma {dma\_op} {data\_amount\_Byte} Byte")

        case \_:

            raise ValueError(command)

command = ('dma','send\_data',256)

op(command)

dma send\_data 256 Byte

# 1. 

a = [['\_']\*3 for i in range(3)]  #创建一个list ，嵌套3个 3长度列表

print(a)

a[1][1]='x'  # 可以单独修改每一个item

print(a)

# 2. 

a=[['\_']\*3]\*3  #创建1个列表， 创建1个3长度列表并复制3份，每份指向同一个引用

print(a)

a[1][1]='x' #修改一个则其余2个都跟着改变

print(a)

[['_', '_', '_'], ['_', '_', '_'], ['_', '_', '_']]

[['_', '_', '_'], ['_', 'x', '_'], ['_', '_', '_']]

[['_', '_', '_'], ['_', '_', '_'], ['_', '_', '_']]

[['_', 'x', '_'], ['_', 'x', '_'], ['_', 'x', '_']]

a=[\_ for \_ in range(4)]

print(id(a))

a+=[45]

print(a)

print(id(a)) # 同一个对象



b=(\_ for \_ in range(4))

print(id(b))

b\*=2  # 这里直接爆了Error ， 而不是书中写的创建一个的b 并赋值

print(id(b))

2000309021312
[0, 1, 2, 3, 45]
2000309021312
2000296589488
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[76], line 9
      7 b=(\_ for \_ in range(4))
      8 print(id(b))
----> 9 b\*=2
     10 print(id(b))
TypeError: unsupported operand type(s) for \*=: 'generator' and 'int'

fruits= ['grape','raspberry','apple','banana']

print(sorted(fruits)) 

print(sorted(fruits,reverse=True))

print(sorted(fruits,key=len))

print(fruits)

print(fruits.sort()) # 返回值为None

print(fruits) #改变了fruits 对象

['apple', 'banana', 'grape', 'raspberry']

['raspberry', 'grape', 'banana', 'apple']

['grape', 'apple', 'banana', 'raspberry']

['grape', 'raspberry', 'apple', 'banana']

None

['apple', 'banana', 'grape', 'raspberry']

from array import array
from random import random
a = array('d',(random() for i in range(2**8)))
print(a[-1])

# 写到一个二进制文件中

fp = open('data.bin','wb')

a.tofile(fp)

fp.close()



# load bin 到array 

b = array('d')

fp = open('data.bin','rb')

b.fromfile(fp,2**8) 

fp.close()

print(b[-1])

0.6979163457345411
0.6979163457345411

from array import array

a = array('B',(range(0,6)))

mem1 = memoryview(a)

mem2 = mem1.cast('B',[2,3])

print(mem2.tolist())

mem3 = mem1.cast('B',[3,2])

print(mem3.tolist())

mem3[1,1]=34

mem2[0,0]=22

print(a) # 共享内存，原始的array 值会改变

[[0, 1, 2], [3, 4, 5]]
[[0, 1], [2, 3], [4, 5]]
array('B', [22, 1, 2, 34, 4, 5])