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【Python】Python3基础

计算机、信息技术与工程 知识笔记 作者 Perrin Yong 约 10 分钟
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【Python】Python3基础

创建时间：2021/5/11 15:02

  • 【Python】Python3基础
    • 知识结构与资料
    • 基础语法特征
      • string
      • list
        • 增删改查
        • 排序，反转，计算长度
        • 遍历，创建，计算
          • for…in
          • range
          • 计算
          • 简单的遍历并处理
          • 截取一部分
      • 元组
      • 字典
        • 遍历
      • 逻辑运算
      • 输入：
      • if-else
      • while
      • 函数
      • class
      • 导入
        • 函数导入
        • 类导入
      • 文件
        • 读取整个文件
        • 逐行读取
        • 写入文件
        • json
      • 异常
    • python3与python2的区别
      • 除法
    • 进阶
      • arbitrary number of arguments
        • **kwargs
      • os.system & os.popen & subprocess
        • os.system
        • os.popen
        • subprocess.Popen
        • 对比
      • Lambda
      • Map
      • filter
      • Iterator & Generator
        • Iterator
        • Generator
          • Building Generators With Generator Expressions
        • 深入理解
        • Profiling Generator Performance
    • 工具与应用
      • Sublime Build Python
    • Ref

知识结构与资料

Alt text

https://docs.python.org/3/ https://docs.pythontab.com/python/python3.5/index.html https://www.liaoxuefeng.com/wiki/1016959663602400 https://www.runoob.com/python3/python3-tutorial.html

快速教程： https://juejin.cn/post/6844903765410070535 https://www.cnblogs.com/wmyskxz/p/12550276.html

基础语法特征

string

用引号括起的都是字符串

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

加号(+)来合并字符串

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

title() - 将每个单词的首字母都改为大写。 upper()、lower()

rstrip() 删除右侧空白 lstrip() 删除左侧空白 strip() 删除两端空白 strip() 不改变原来的字符串

str() - 将数字转换为字符串再进行拼接

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

list

方括号([])来表示列表，并用逗号来分隔其中的元素

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

增删改查

修改元素直接用索引修改

在末尾添加：append

插入：insert

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

del：按索引删除 pop()：删除列表最后一个元素并返回最后一个元素的值。 pop(index) - 传索引删除任意位置的值并返回 remove()：按值删除第一个元素

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

list[-2] 是获取倒数第二个元素

排序，反转，计算长度

改变原列表： list.sort() list.sort(reverse=True) - 反转

不影响原始排列顺序： sorted(list) sorted(list, reverse=True)

list.reverse()

len(list)

遍历，创建，计算

for…in
string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");
range

range(1,6) - 前闭后开

range(0,11,2) - 指定步长为2

计算

min()：计算最小值 max()：计算最大值 sum()：计算总和

简单的遍历并处理
string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");
截取一部分

前闭后开

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

如果使用 names3=names，则只是把引用（地址）赋值过去，指向的是用一份数据。

元组

不可变的列表被称为元组 圆括号标识 访问和遍历方式与列表一致

字典

可将任何Python对象用作字典中的值

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

遍历

遍历所有键值对 items()

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

遍历所有键 for k in cats.keys() for k in cats

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

没有顺序

遍历所有值 values()

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

遍历并去除重复项 set() for value in set(cat.values())

可以在列表中嵌套字典、在字典中嵌套列表以及在字典中嵌套字典。

逻辑运算

  • and

  • or

  • in - 判断列表是否包含某元素

  • not in - 判断不包含

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

输入：

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

if-else

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

while

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

for…in else

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

pass 不做任何事情，一般用做占位语句

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

函数

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

传递任意数量的实参

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

  • 函数名应只包含小写字母和下划线

  • 给形参指定默认值时，等号两边不要有空格

class

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

导入

函数导入

cat.py

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

import cat import cat as c

from cat import eat, run from cat import eat as cat_eat

from cat import * #不推荐。避免同名函数覆盖

要么只导入你需要使用的函数，要么导入整个模块并使用句点表示法。

类导入

假如 car.py 包含了三个类 Car ， Battery 和 ElectricCar 。

import car from car import Car, ElectricCar from module_name import * #不推荐

文件

with - 在不再需要访问文件后将其关闭。有了 with 你只管打开文件，并在需要时使用它，Python自会 在合适的时候自动将其关闭。 open() - 用于打开一个文件，参数为文件的路径。文件路径可以是相对路径，也可以是绝对路径。

读取整个文件

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

相比于原始文件，该输出唯一不同的地方是末尾多了一个空行。为何会多出这个空行呢?因为 read() 到达文件末尾时返回一个空字符串，而将这个空字符串显示出来时就是一个空行。要删除多出来的空行，可在print语句中使用 rstrip()。

逐行读取

要以每次一行的方式检查文件，可对文件对象使用for循环。

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

写入文件

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

  • r ：只读。

  • w : 只写。如果文件不存在则创建，如果文件存在则先清空，再写入。

  • a ：附加模式，写入的内容追加到原始文件后面。如果文件不存在则创建。

  • r+ ：可读可写。

json

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

异常

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

python3与python2的区别

除法

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

进阶

arbitrary number of arguments

The non keyword arguments are passed as a tuple and these passed arguments make tuple inside the function with same name as the parameter excluding asterisk *.

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

**kwargs

The arguments are passed as a dictionary

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

os.system & os.popen & subprocess

os.system

同步调用（阻塞）

  • os.system方法是os模块最基础的方法，其它的方法一般在该方法基础上封装完成。

  • 创建一个子进程在系统上执行命令行，子进程的执行结果无法影响主进程。

  • 返回值是脚本的退出状态码，0表示成功，其他均为失败

坑点：

  1. 连续几个system命令执行，是启动了多个子进程来运行，上一条 cd 的效果不会在下一个子进程中生效。

Alt text

  1. os.system(command) 在调用完shell脚本后，返回一个16位的二进制数，低位为杀死所调用脚本的信号号码，高位为脚本的退出状态码，即脚本中“exit 1”的代码执行后，os.system函数返回值的高位数则是1，如果低位数是0的情况下，则函数的返回值是0x0100,换算为十进制得到256。

os.popen

非阻塞

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

command – 使用的命令。 mode – 模式权限可以是 ‘r’(默认) 或 ‘w’。 bufsize – 指明了文件需要的缓冲大小：0意味着无缓冲；1意味着行缓冲；

返回一个文件描述符号为fd的打开的文件对象。

read()、eadlines()、close() 会产生阻塞效果。 文件用完就应该关闭 。使用如下方法会自动关闭

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

像调用”ls”这样的shell命令，应该使用popen的方法来获得内容，对比如下：

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

subprocess.Popen

可以用 wait 来等待命令执行完成

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

当test.txt大于64k时，会阻塞住。原因是，子进程产生一些数据，他们会被buffer起来，当buffer满了，会写到子进程的标准输出和标准错误输出，这些东西通过管道发送给父进程。当管道满了之后，子进程就停止写入，于是就卡住了。

解决方法：

  1. 在wait前，读取管道，这样管道就不会满
string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");
  1. 使用communicate
string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

对比

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

Lambda

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

Map

将函数应用于各种数据结构中的元素

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

filter

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

Iterator & Generator

Iterator

An iterator is an object that can be iterated upon, meaning that you can traverse through all the values.

Iterator vs Iterable： Lists, tuples, dictionaries, and sets are all iterable objects. They are iterable containers which you can get an iterator from.

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

Looping Through an Iterator: We can also use a for loop to iterate through an iterable object.

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

Create an Iterator

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

Generator

在 Python 中，使用了 yield 的函数被称为生成器函数（generator functions）。 Introduced with PEP 255, generator functions are a special kind of function that return a lazy iterator. These are objects that you can loop over like a list. However, unlike lists, lazy iterators do not store their contents in memory.

在调用生成器运行的过程中，每次遇到 yield 时函数会暂停并保存当前所有的运行信息，返回 yield 的值, 并在下一次执行 next() 方法时从当前位置继续运行。

Example: Generating an Infinite Sequence

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");
Building Generators With Generator Expressions
string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

深入理解

python的yield关键字与C#类似。函数中有yield语句时，调用该函数，会返回一个迭代器，并不会真正执行该函数。首次，对该函数调用next时，函数开始执行，会尝试执行到第一次yield语句，获取返回值。如果在调用到yield语句之前，函数返回，则会抛出异常 StopIteration 。如果成功执行到yield语句并返回，再次调用next函数时，会从这个yield语句的下一个语句开始执行。

示例如下，调用recv，会返回一个generator对象，调用next时，函数开始执行。而起初在调用时，会执行到break并返回，无法执行到yield，next函数会抛出异常，无法继续遍历。直到满足条件，可以执行到yield时，调用next才会获取到返回值 cnt ，下次调用next时，本次yield语句后的一个语句开始执行。

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

输出如下：

Alt text

Profiling Generator Performance

string str1 = String.Empty;
string str2 = String.Empty;

str2 = String.Intern(sb.ToString());

if((object)str1==(object)str2)
    Console.WriteLine("The strings are equal.");
else
    Console.WriteLine("The strings are not equal.");

工具与应用

https://www.zhihu.com/question/24590883/answer/1220720307

Sublime Build Python

https://blog.csdn.net/github_36601823/article/details/69218197

Ref

https://www.zhihu.com/question/300985609/answer/1225638751 https://juejin.cn/post/6844903765410070535 https://www.cnblogs.com/yu97271486/p/12497622.html https://www.jianshu.com/p/62f0b9a3dd3e https://www.w3schools.com/python/python_iterators.asp https://realpython.com/introduction-to-python-generators/