自学教程：python3.9之你应该知道的新特性详解

>> '"Isn/'t," they said.''"Isn/'t," they said.'>>> print('"Isn/'t," they said.')"Isn't," they said.>>> s = 'First line./nSecond line.'  # /n means newline>>> s  # without print(), /n is included in the output'First line./nSecond line.'>>> print(s)  # with print(), /n produces a new lineFirst line.Second line.

>>> print('C:/some/name')  # h这里的/n会被认为是转义字符C:/someame>>> print(r'C:/some/name')  #在转义之前标记为rC:/some/name

>>>3 * 'mmm'  + ‘qqq'>'mmmmmmmmmqqq'

>>>'Py' 'thon'>‘Python'

>>>('Put several strings within parentheses '...         'to have them joined together.')>>>text>'Put several strings within parentheses to have them joined together.'

>>> prefix = 'Py'>>> prefix 'thon'  # can't concatenate a variable and a string literal  File "<stdin>", line 1    prefix 'thon'                ^SyntaxError: invalid syntax>>> ('un' * 3) 'ium'  File "<stdin>", line 1    ('un' * 3) 'ium'                   ^SyntaxError: invalid syntax

>>> prefix + 'thon''Python'

str[0]  str[1]  str[-1]#为什么反向索引从-1开始?#-0 和 0 相等，指向的是同一个值。

>>> word[0] 'P'>>> word[2:5] 'tho'

>>> word[:2] + word[2:]'Python'>>> word[:4] + word[4:]'Python'

>>> word[4:42]'on'>>> word[42:]''

#补充：深拷贝和浅拷贝的区别：#使用浅拷贝，当原容器对象中可变对象中有元素发生变化，拷贝得到的对象也会变#化。而使用深拷贝时，不会有这种问题。#!/usr/bin/python# -*- coding:utf-8 -*-# @Author : qmt# @Time : 2021/4/27 21:26import copy# 浅拷贝list1 = [[1,1], 555 , 'mm']list2 = list1.copy()list3 = copy.copy(list1)print(id(list1))print(id(list2))print(id(list3))# 输出结果# 2207574630976# 2207574779456# 2207574778816print(id(list1[0]))print(id(list2[0]))# 输出结果：# 2287435172736# 2287435172736print(id(list1[1]))print(id(list2[1]))# 输出结果：# 2085715335536# 2085715335536print(id(list1[2]))print(id(list2[2]))print(id(list3[2]))# 输出结果：# 3009054756720# 3009054756720# 3009054756720# 改变第一个值，查看复制对象的变化list1[0][0] = 100print(list1)print(list2)print(list3)# 输出结果：# [[100, 1], 555, 'mm']# [[100, 1], 555, 'mm']# [[100, 1], 555, 'mm']list1[2] = 32print(list1)print(list2)print(list3)# 输出结果：# [[100, 1], 555, 32]# [[100, 1], 555, 'mm']# [[100, 1], 555, 'mm']# 字符串是不可变对象，所以浅拷贝不会同步到其他复制对象中list1[1] = 'mm'print(list1)print(list2)print(list3)# 输出结果：# [[100, 1], 'mm', 32]# [[100, 1], 555, 'mm']# [[100, 1], 555, 'mm']

#!/usr/bin/python# -*- coding:utf-8 -*-# @Author : qmt# @Time : 2021/4/27 21:35import copylist1 = [[1,2],'mm',2222]list2 = copy.deepcopy(list1)print(id(list1))print(id(list2))# 输出结果：指向不同的内存地址# 2847485493888# 2847485646528list1[0][0] = 100print(id(list1))print(id(list2))# 输出结果：list2作为一个深拷贝对象，内存地址并没有发生变化# 1368800613056# 1368800441920list1[2] = 100print(list1)print(list2)# 输出结果：list1的任何操作都不会对list2产生影响，因为这相当于创建了一个新的对象[[100, 2], 'mm', 100][[1, 2], 'mm', 2222]

import copya = (1,2)b = copy.copy(a)c =copy.deepcopy(a)print(b == c)print(id(b)==id(c))lista = [5,6]listb = copy.copy(lista)listc = copy.copy(lista)print(listb == listc)print(id(lista) == id(listb))

Python中的对象包含三个基本要素，分别是：id：用来唯一标识一个对象，可以理解为内存地址；type：标识对象的类型；value：对象的值；== ：比较两个对象的内容是否相等，即两个对象的 value 是否相等，无论 id 是否相等，默认会调用对象的 __eq__()方法is： 比较的是两个对象是不是完全相同，即他们的 id 要相等。也就是说如果  a is b  为 True，那么 a == b 也为True

for n in range(2,10):    for x in range(2,n):        if n % x == 0:            print(n ,'equals',x ,'*', n//x)            break    else:        print(n,'is a prime number')