python程序练习

import numpy as np

生成元素全为0的二维张量，两个维度分别为３，４

np.zeros((3,4))

array([[0., 0., 0., 0.],
       [0., 0., 0., 0.],
       [0., 0., 0., 0.]])

生成三维的随机张量，三个维度分别为２,3,4

np.random.rand(2,3,4)

array([[[0.1477983 , 0.40141709, 0.85224419, 0.38584974],
        [0.24829636, 0.27591131, 0.26122221, 0.2995639 ],
        [0.93788947, 0.72531966, 0.27450982, 0.37431617]],

       [[0.92417031, 0.98691281, 0.29320554, 0.5915986 ],
        [0.76867925, 0.40096397, 0.31562832, 0.59135643],
        [0.60332   , 0.48597609, 0.8636971 , 0.39562407]]])

方阵：行数和列数相等的矩阵

np.eye(4)

array([[1., 0., 0., 0.],
       [0., 1., 0., 0.],
       [0., 0., 1., 0.],
       [0., 0., 0., 1.]])

reshape：在数学中并没有reshape运算，但是在Numpy和Tensorflow等运算库中是一个非常常用的运算，用来改变一个张量的维度数和每个维度的大小，例如一个10x10的图片在保存时直接保存为一个包含100个元素的序列，在读取后就可以使用reshape将其从1x100变换为10x10，示例如下

x= np.arange(12)

生成一个包含整数0-11的向量

x

array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11])

x.shape

(12,)

x = x.reshape(1,12)

x

array([[ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11]])

x= x.reshape(3,4)

x

array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])

x = np.arange(5).reshape(1,-1)

x

array([[0, 1, 2, 3, 4]])

x.T

array([[0],
       [1],
       [2],
       [3],
       [4]])

A = np.arange(12).reshape(3,4)

A

array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])

A.T

array([[ 0,  4,  8],
       [ 1,  5,  9],
       [ 2,  6, 10],
       [ 3,  7, 11]])

生成234的张量

B = np.arange(24).reshape(2,3,4)

B

array([[[ 0,  1,  2,  3],
        [ 4,  5,  6,  7],
        [ 8,  9, 10, 11]],

       [[12, 13, 14, 15],
        [16, 17, 18, 19],
        [20, 21, 22, 23]]])

将B的01 两个维度转置

B.transpose(1,0,2)

array([[[ 0,  1,  2,  3],
        [12, 13, 14, 15]],

       [[ 4,  5,  6,  7],
        [16, 17, 18, 19]],

       [[ 8,  9, 10, 11],
        [20, 21, 22, 23]]])

 x = np.ones((1, 2, 3))

x

array([[[1., 1., 1.],
        [1., 1., 1.]]])

x.shape

(1, 2, 3)

np.transpose(x,(1,0,2))

array([[[1., 1., 1.]],

       [[1., 1., 1.]]])

np.transpose(x,(1,0,2)).shape

(2, 1, 3)

A= np.arange(6).reshape(3,2)

B = np.arange(6).reshape(2,3)

A

array([[0, 1],
       [2, 3],
       [4, 5]])

B

array([[0, 1, 2],
       [3, 4, 5]])

np.matmul(A,B)

array([[ 3,  4,  5],
       [ 9, 14, 19],
       [15, 24, 33]])

A = np.arange(6).reshape(3,2)

A

array([[0, 1],
       [2, 3],
       [4, 5]])

A*A

array([[ 0,  1],
       [ 4,  9],
       [16, 25]])

A+A

array([[ 0,  2],
       [ 4,  6],
       [ 8, 10]])

A= np.arange(4).reshape(2,2)

A

array([[0, 1],
       [2, 3]])

np.linalg.inv(A)

array([[-1.5,  0.5],
       [ 1. ,  0. ]])

字符串列表拼接

seeds = ["sesame","sunflower"]

seeds += ["pumpkin"]

seeds

['sesame', 'sunflower', 'pumpkin']

m = [5,9]

m += [6]

m

[5, 9, 6]

seeds += [5]

seeds

['sesame', 'sunflower', 'pumpkin', 5]

seeds.append("durian")

seeds

['sesame', 'sunflower', 'pumpkin', 5, 'd', 'u', 'r', 'i', 'a', 'n', 'durian']

print("Type integers,each followed by Enter; or just Enter to finish")
total = 0
count = 0
while True:
    line = input("Integer: ")
    if line:
        try:
            number =int(line)
        except ValueError as err:
            print(err)
            continue
        total += number
        count += 1
    else:
        break
if count:
    print("count=",count, "total =", total,"mean=", total/count)

Type integers,each followed by Enter; or just Enter to finish
Integer: 3
Integer: 4
Integer: a
invalid literal for int() with base 10: 'a'
Integer: 
count= 2 total = 7 mean= 3.5

函数的创建与调用

def functionName(arguments):

suite

def get_int(msg = 0):
    while True:
        try:
            i=int(input(msg))
            return i
        except ValueError as err:
            print(err)

get_int()

03





3

age = get_int("enter your age:")

enter your age:23

import sys

print(sys.argv)

['C:\\ProgramData\\Anaconda3\\lib\\site-packages\\ipykernel_launcher.py', '-f', 'C:\\Users\\acer\\AppData\\Roaming\\jupyter\\runtime\\kernel-c140e89f-7532-424b-a3fc-8811de1dff5c.json']

模块中函数调用格式为 moduleName.functionName(arguments)

import random

x = random.randint(1,6)

x

2

x

2

x

2

x

2

x = random.randint(1,6)

x

1

y =random.choice(["apple","banana","cherry","durian"])

y

'apple'

y =random.choice(["apple","banana","cherry","durian"])

y

'durian'

y

'apple'

"917.5".isdigit()

False

"203".isdigit()

True

"-2".isdigit()

False

record ="Leo Tolstoy*1828-8-28*1910-11-20"

fields =record.split("*")

fields

['Leo Tolstoy', '1828-8-28', '1910-11-20']

born = fields[1].split("-")

born

['1828', '8', '28']

died = fields[2].split("-")
died

['1910', '11', '20']

print("lived about",int(died[0])- int(born[0]),"years")

lived about 82 years

"The novel '{0}' was published in {1}".format("Hard Times",1854)

"The novel 'Hard Times' was published in 1854"

"{who} turned {age} this year".format(who="She",age=88)

'She turned 88 this year'

"The {who} was {0} last week".format(12,who="boy")

'The boy was 12 last week'

stock =["paper","envelopes","notepads","pens","paper clips"]

"We have {0[1]} and {0[2]} in stock".format(stock)

'We have envelopes and notepads in stock'

d= dict(animal="elephant",weight=12000)

"The {0[animal]} weighs {0[weight]}kg".format(d)

'The elephant weighs 12000kg'

element = "Silver"
number = 47
"Element {number} is {element}".format(**locals())

'Element 47 is Silver'

"The {animal} weighs {weight}kg".format(**d)

'The elephant weighs 12000kg'

import decimal
decimal.Decimal("3.4084")

Decimal('3.4084')

print(decimal.Decimal("3.4084"))

3.4084

def f(x):
    return x,x **2

for x,y in ((1,1),(2,4),(3,9)):
    print(x,y)

1 1
2 4
3 9

things = (1,-7.5,("pea",(5,"Xyz"),"queue"))
things[2][1][1]

'Xyz'

things[2][1][1][2]

'z'

MANUFACTURER,MODEL,SEATING =(0,1,2)

MANUFACTURER

0

a,b =(3,4)

a,b = (b,a)

a,b

(4, 3)

import math

math.hypot(3,4) # 求两点之间的距离

5.0

import collections

Sale = collections.namedtuple("Sale","productid customerid date quantity price")

Sale

__main__.Sale

sales =[]
sales.append(Sale(432,921,"2008-09-14",3,7.99))

sales.append(Sale(419,874,"2008-09-15",1,18.49))

total = 0
for sale in sales:
    total += sale.quantity * sale.price
print("Total ${0:.2f}".format(total))

Total $42.46

Aircraft = collections.namedtuple("Aircraft","manufacturer model seating")

Seating = collections.namedtuple("Seating","minimum maximum")

aircraft =Aircraft("Airbus","A320-200",Seating(100,220))

aircraft

Aircraft(manufacturer='Airbus', model='A320-200', seating=Seating(minimum=100, maximum=220))

aircraft.seating.maximum

220

print("{0} {1}".format(aircraft.manufacturer,aircraft.model))

Airbus A320-200

"{0.manufacturer} {0.model}".format(aircraft)

'Airbus A320-200'

"{manufacturer} {model}".format(**aircraft._asdict())

'Airbus A320-200'

first,*rest =[9,2,-4,8,7] # 带星号表达式

first,rest

(9, [2, -4, 8, 7])

first,*mid,last = "Charles Philip Arthur George Windsor".split()

first,mid,last

('Charles', ['Philip', 'Arthur', 'George'], 'Windsor')

x= 8143 

x

8143

del x

L =["yes","my","name"]

for i in range(len(L)):
    print(L[i])

yes
my
name

a = range(len(L))

a

range(0, 3)

numbers =[1,2,3,4]

for i in range(len(numbers)):
    numbers[i] += 1

numbers

[2, 3, 4, 5]