Python 简明教程

Python - Environment Setup

学习 Python 的第一步是在您的机器上安装它。如今，大多数计算机，尤其是装有 Linux 操作系统，都预装了 Python。但它可能不是最新版本。

First step in the journey of learning Python is to install it on your machine. Today most computer machines, especially having Linux OS, have Python pre-installed. However, it may not be the latest version.

Python 可用于各种平台，包括 Linux 和 Mac OS X。让我们了解如何设置我们的 Python 环境。

Python is available on a wide variety of platforms including Linux and Mac OS X. Let’s understand how to set up our Python environment.

Unix (Solaris, Linux, FreeBSD, AIX, HP/UX, SunOS, IRIX, etc.)
Win 9x/NT/2000
Macintosh (Intel, PPC, 68K)
OS/2
DOS (multiple versions)
PalmOS
Nokia mobile phones
Windows CE
Acorn/RISC OS
BeOS
Amiga
VMS/OpenVMS
QNX
VxWorks
Psion

Python 也已移植到 Java 和 .NET 虚拟机

Python has also been ported to the Java and .NET virtual machines

Local Environment Setup

打开一个终端窗口，并键入 "python" 以了解它是否已安装以及安装的是哪个版本。如果已安装 Python，那么你将收到如下信息：

Open a terminal window and type "python" to find out if it is already installed and which version is installed. If Python is already installed then you will get a message something like as follows:

$ python
Python 3.11.2 (main, Feb 8 2023, 14:49:24) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

>>>

Downloading Python

最新的源代码、二进制文件、文档、新闻等信息可在 Python 官方网站 https://www.python.org/ 上获取。

The most up-to-date and current source code, binaries, documentation, news, etc., is available on the official website of Python https://www.python.org/

你可以从 https://www.python.org/doc/ 下载 Python 文档。文档提供 HTML、PDF 和 PostScript 格式。

You can download Python documentation from https://www.python.org/doc/. The documentation is available in HTML, PDF, and PostScript formats.

Installing Python

Python 发行版可用于各种平台。你只需下载适用于你的平台的二进制代码并安装 Python。

Python distribution is available for a wide variety of platforms. You need to download only the binary code applicable for your platform and install Python.

如果你的平台没有二进制代码，你需要 C 编译器来手动编译源代码。编译源代码在安装中所需特性的选择方面提供了更大的灵活性。

If the binary code for your platform is not available, you need a C compiler to compile the source code manually. Compiling the source code offers more flexibility in terms of choice of features that you require in your installation.

以下是对在各种平台上安装 Python 的快速概述 −

Here is a quick overview of installing Python on various platforms −

Install Python on Ubuntu Linux

要检查 Python 是否已安装，请打开 Linux 终端并输入以下命令：

To check whether Python is already installed, open the Linux terminal and enter the following command −

$ python3.11 --version

在 Ubuntu Linux 中，安装 Python 最简单的方法是使用 apt – Advanced Packaging Tool 。建议始终更新所有配置存储库中的包列表。

In Ubuntu Linux, the easiest way to install Python is to use apt – Advanced Packaging Tool. It is always recommended to update the list of packages in all the configured repositories.

$ sudo apt update

即使更新后，根据您正在使用的 Ubuntu 版本，最新版本的 Python 可能仍不可用。若要克服此问题，请添加 deadsnakes 存储库。

Even after the update, the latest version of Python may not be available for install, depending upon the version of Ubuntu you are using. To overcome this, add the deadsnakes repository.

$ sudo apt-get install software-properties-common
$ sudo add-apt-repository ppa:deadsnakes/ppa

再次更新软件包列表。

Update the package list again.

$ sudo apt update

要安装最新的 Python 3.11 版本，请在终端中输入以下命令：

To install the latest Python 3.11 version, enter the following command in the terminal −

$ sudo apt-get install python3.11

检查是否已正确安装。

Check whether it has been properly installed.

$ python3
Python 3.11.2 (main, Feb 8 2023, 14:49:24) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

>>> print ("Hello World")
Hello World

>>>

Install Python on other Linux

以下是在 Unix/Linux 计算机上安装 Python 的简单步骤。

Here are the simple steps to install Python on Unix/Linux machine.

Open a Web browser and go to https://www.python.org/downloads/.
Follow the link to download zipped source code available for Unix/Linux.
Download and extract files.
Editing the Modules/Setup file if you want to customize some options.

现在发出以下命令：

Now issue the following commands:

$ run ./configure script
$ make
$ make install

这会在标准位置 /usr/local/bin 中安装 Python，并在 /usr/local/lib/pythonXX 中安装其库，其中 XX 是 Python 的版本。

This installs Python at standard location /usr/local/bin and its libraries at /usr/local/lib/pythonXX where XX is the version of Python.

Using Yum Command

Red Hat Enterprise Linux (RHEL 8) 默认不安装 Python 3。我们通常在 CentOS 上使用 yum 命令和其他相关的变体。在 RHEL 8 上安装 Python 3 的步骤如下：

Red Hat Enterprise Linux (RHEL 8) does not install Python 3 by default. We usually use yum command on CentOS and other related variants. The procedure for installing Python-3 on RHEL 8 is as follows:

$ sudo yum install python3

Install Python on Windows

需要注意的是，Python 版本 3.10 及更高版本无法安装在 Windows 7 或更早的操作系统上。

It should be noted that Python’s version 3.10 onwards cannot be installed on Windows 7 or earlier operating systems.

安装 Python 的推荐方法是使用官方安装程序。首页上给出了最新稳定版本链接。它也在 https://www.python.org/downloads/windows/. 处找到。

The recommended way to install Python is to use the official installer. A link to the latest stable version is given on the home page itself. It is also found at https://www.python.org/downloads/windows/.

您可以找到 32 位和 64 位架构的可嵌入软件包和安装程序。

You can find embeddable packages and installers for 32 as well as 64-bit architecture.

让我们下载 64 位 Windows 安装程序：

Let us download 64-bit Windows installer −

( https://www.python.org/ftp/python/3.11.2/python-3.11.2-amd64.exe )

(https://www.python.org/ftp/python/3.11.2/python-3.11.2-amd64.exe)

双击下载文件所在的位置以开始安装。

Double click on the file where it has been downloaded to start the installation.

虽然您可以直接单击“立即安装”按钮继续进行，但建议选择路径较短的安装文件夹，并勾选第二个复选框以更新 PATH 变量。

Although you can straight away proceed by clicking the Install Now button, it is advised to choose the installation folder with a relatively shorter path, and tick the second check box to update the PATH variable.

接受此安装向导中其余步骤的默认设置以完成安装。

Accept defaults for rest of the steps in this installation wizard to complete the installation.

打开窗口命令提示符终端并运行 Python 以检查安装是否成功。

Open the Window Command Prompt terminal and run Python to check the success of installation.

C:\Users\Acer>python
Python 3.11.2 (tags/v3.11.2:878ead1, Feb 7 2023, 16:38:35) [MSC v.1934
64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Python 的标准库有一个名为 IDLE 的可执行模块—— Integrated Development and Learning Environment 的简称。从 Windows 开始菜单中找到它然后启动。

Python’s standard library has an executable module called IDLE – short for Integrated Development and Learning Environment. Find it from Window start menu and launch.

IDLE 包含 Python 外壳（交互式解释器）和一个可自定义的多窗口文本编辑器，具有语法突出显示、智能缩进、自动补全等功能。它是跨平台的，因此在 Windows、MacOS 和 Linux 上工作方式相同。它还有一个调试器，可以设置断点、步进和查看全局和局部命名空间。

IDLE contains Python shell (interactive interpreter) and a customizable multi-window text editor with features such as syntax highlighting, smart indent, auto completion etc. It is cross-platform so works the same on Windows, MacOS and Linux. It also has a debugger with provision to set breakpoints, stepping, and viewing of global and local namespaces.

以下是如何在 Windows 机器上安装 Python：

Here are the steps to install Python on Windows machine.

Open a Web browser and go to https://www.python.org/downloads/.
Follow the link for the Windows installer python-XYZ.msi file where XYZ is the version you need to install.
To use this installer python-XYZ.msi, the Windows system must support Microsoft Installer 2.0. Save the installer file to your local machine and then run it to find out if your machine supports MSI.
Run the downloaded file. This brings up the Python install wizard, which is really easy to use. Just accept the default settings, wait until the install is finished, and you are done.

Macintosh Installation

新近的 Mac 上都预装了 Python，但可能已过时很多年。请参阅 http://www.python.org/download/mac/ 以获取有关获取 Mac 上支持开发的其他工具的当前版本的说明。对于 Mac OS X 10.3（在 2003 年发布）之前的旧 Mac 操作系统，可以使用 MacPython。

Recent Macs come with Python installed, but it may be several years out of date. See http://www.python.org/download/mac/ for instructions on getting the current version along with extra tools to support development on the Mac. For older Mac OS’s before Mac OS X 10.3 (released in 2003), MacPython is available.

由 Jack Jansen 维护，您可以在他的网站上完全访问完整的文档 − 链接：http://www.cwi.nl/ _{jack/macpython.html[http://www.cwi.nl/} jack/macpython.html]。您可以找到 Mac OS 安装的完整安装详细信息。

Jack Jansen maintains it and you can have full access to the entire documentation at his website − http://www.cwi.nl/jack/macpython.html. You can find complete installation details for Mac OS installation.

Setting up PATH

程序和其他可执行文件可以位于许多目录中，因此操作系统会提供一个搜索路径，其中列出了操作系统搜索可执行文件的目录。

Programs and other executable files can be in many directories, so operating systems provide a search path that lists the directories that the OS searches for executables.

路径存储在环境变量中，该变量是由操作系统维护的一个已命名字符串。此变量包含可供命令 shell 和其他程序使用的信息。

The path is stored in an environment variable, which is a named string maintained by the operating system. This variable contains information available to the command shell and other programs.

path 变量在 Unix 中被命名为 PATH，在 Windows 中被命名为 Path（Unix 区分大小写；Windows 不区分大小写）。

The path variable is named as PATH in Unix or Path in Windows (Unix is case sensitive; Windows is not).

在 Mac OS 中，安装程序会处理路径详细信息。要从任何特定目录调用 Python 解释器，您必须将 Python 目录添加到您的路径中。

In Mac OS, the installer handles the path details. To invoke the Python interpreter from any particular directory, you must add the Python directory to your path.

Setting path at Unix/Linux

要在 Unix 中为特定会话将 Python 目录添加到路径中 −

To add the Python directory to the path for a particular session in Unix −

In the csh shell − type setenv PATH "$PATH:/usr/local/bin/python" and press Enter.
In the bash shell (Linux) − type export PATH="$PATH:/usr/local/bin/python" and press Enter.
In the sh or ksh shell − type PATH="$PATH:/usr/local/bin/python" and press Enter.
Note − /usr/local/bin/python is the path of the Python directory

Setting path at Windows

要在Windows特定会话的路径中添加Python目录：

To add the Python directory to the path for a particular session in Windows −

At the command prompt - 键入 path %path%;C:\Python 并按回车。

At the command prompt − type path %path%;C:\Python and press Enter.

Note - C:\Python是Python目录的路径

Note − C:\Python is the path of the Python directory

Python Environment Variables

以下是Python可以识别的重要环境变量：

Here are important environment variables, which can be recognized by Python −

Sr.No.	Variable & Description
1	PYTHONPATH It has a role similar to PATH. This variable tells the Python interpreter where to locate the module files imported into a program. It should include the Python source library directory and the directories containing Python source code. PYTHONPATH is sometimes preset by the Python installer.
2	PYTHONSTARTUP It contains the path of an initialization file containing Python source code. It is executed every time you start the interpreter. It is named as .pythonrc.py in Unix and it contains commands that load utilities or modify PYTHONPATH.
3	PYTHONCASEOK It is used in Windows to instruct Python to find the first case-insensitive match in an import statement. Set this variable to any value to activate it.
4	PYTHONHOME It is an alternative module search path. It is usually embedded in the PYTHONSTARTUP or PYTHONPATH directories to make switching module libraries easy.

Running Python

有三种不同的方法可用于启动Python：

There are three different ways to start Python −

Interactive Interpreter

您可以从Unix、DOS或任何其他提供命令行解释器或shell窗口的系统启动Python。

You can start Python from Unix, DOS, or any other system that provides you a command-line interpreter or shell window.

在命令行中输入 python 。

Enter python the command line.

在交互式解释器中立即开始编码。

Start coding right away in the interactive interpreter.

$python # Unix/Linux
or
python% # Unix/Linux
or
C:> python # Windows/DOS

以下是所有可用命令行选项的列表：

Here is the list of all the available command line options −

Sr.No.	Option & Description
1	-d It provides debug output.
2	-O It generates optimized bytecode (resulting in .pyo files).
3	-S Do not run import site to look for Python paths on startup.
4	-v verbose output (detailed trace on import statements).
5	-X disable class-based built-in exceptions (just use strings); obsolete starting with version 1.6.
6	-c cmd run Python script sent in as cmd string
7	file run Python script from given file

Script from the Command-line

可通过 invoking the interpreter on your application，在命令行中执行 Python 脚本，如下所示：

A Python script can be executed at command line by invoking the interpreter on your application, as in the following −

$python script.py # Unix/Linux

or

python% script.py # Unix/Linux

or

C: >python script.py # Windows/DOS

Note − 确保文件权限模式允许执行。

Note − Be sure the file permission mode allows execution.

Integrated Development Environment

如果系统上的 GUI 应用程序支持 Python，您还可以从图形用户界面 (GUI) 环境中运行 Python。

You can run Python from a Graphical User Interface (GUI) environment as well, if you have a GUI application on your system that supports Python.

Unix − IDLE is the very first Unix IDE for Python.
Windows − PythonWin is the first Windows interface for Python and is an IDE with a GUI.
Macintosh − The Macintosh version of Python along with the IDLE IDE is available from the main website, downloadable as either MacBinary or BinHex’d files.

如果您无法正确设置环境，则可以向系统管理员寻求帮助。确保 Python 环境已正确设置，并且运行正常。

If you are not able to set up the environment properly, then you can take help from your system admin. Make sure the Python environment is properly set up and working perfectly fine.

我们提供了 Python Online Compiler/Interpreter ，它可以帮助您直接从浏览器 Edit 和 Execute 代码。尝试点击图标运行以下 Python 代码，以打印常规的“Hello, World!”。

We have provided Python Online Compiler/Interpreter which helps you to Edit and Execute the code directly from your browser. Try to click the icon to run the following Python code to print conventional "Hello, World!".

# This is my first Python program.
# This will print 'Hello, World!' as the output

print ("Hello, World!");