Python 2.7 Tutorial —— 开胃菜
时间：2010-09-19 来源：March.Liu
.. _tut-intro:
********************************* Whetting Your Appetite 开胃菜 *********************************
If you do much work on computers, eventually you find that there's some task you'd like to automate. For example, you may wish to perform a search-and-replace over a large number of text files, or rename and rearrange a bunch of photo files in a complicated way. Perhaps you'd like to write a small custom database, or a specialized GUI application, or a simple game.
如果你要在计算机上做大量的工作，希望它们能够自动化一些。例如，你想在大 量的文本文件中进行查找替换，或者通过复杂的方式将一批图像文件重命名，修 改尺寸。可能你想写一个小型的定制数据库，或者特定的 GUI 应用程序，或者 一个简单的游戏。
If you're a professional software developer, you may have to work with several C/C++/Java libraries but find the usual write/compile/test/re-compile cycle is too slow. Perhaps you're writing a test suite for such a library and find writing the testing code a tedious task. Or maybe you've written a program that could use an extension language, and you don't want to design and implement a whole new language for your application.
如果你是专业的软件开发者，可能会想使用一些 C/C++/Java 库，但是发现通常 的编写/编译/测试/重编译循环太慢了。也许你想为每个写一个测试，可这样做 太麻烦。或者你需要写一个带有扩展语言的程序，可不想为你的应用程序设计和 实现一个新的语言。
Python is just the language for you.
Python 就是你需要的语言。
You could write a Unix shell script or Windows batch files for some of these tasks, but shell scripts are best at moving around files and changing text data, not well-suited for GUI applications or games. You could write a C/C++/Java program, but it can take a lot of development time to get even a first-draft program. Python is simpler to use, available on Windows, Mac OS X, and Unix operating systems, and will help you get the job done more quickly.
你也可以写一个 Unix shell 脚本或者 Windows 批处理文件完成任务，不过 shell 脚本最擅长移动文件和修改文本数据，不擅长编写图形界面的应用程序或 游戏。你可以写个 C/C++/Java 程序，但是就算也一个最简单的草案，也要花 费太多的开发时间。 Python 更易用，并且在 Windows， Mac OS X 和 Unix 操 作系统上可用，能够帮你更快的完成任务。
Python is simple to use, but it is a real programming language, offering much more structure and support for large programs than shell scripts or batch files can offer. On the other hand, Python also offers much more error checking than C, and, being a *very-high-level language*, it has high-level data types built in, such as flexible arrays and dictionaries. Because of its more general data types Python is applicable to a much larger problem domain than Awk or even Perl, yet many things are at least as easy in Python as in those languages.
Python 简单易用，但它是真正的编程语言，比起 shell 脚本或批处理文件，可 以提供更多对大型程序的构造和支持。另一方面，Python 比起C，提供更多的错 误检查。而且作为 *非常高级的编程语言* ，它内置了类似变长数组和字典这样 的高级数据结构。Python 提供了更为通用的数据类型，所以它比 Awk 甚至 Perl 适合更广大的问题领域，做其它的很多事，Python 至少也不会比别的编程语言更复杂。
Python allows you to split your program into modules that can be reused in other Python programs. It comes with a large collection of standard modules that you can use as the basis of your programs --- or as examples to start learning to program in Python. Some of these modules provide things like file I/O, system calls, sockets, and even interfaces to graphical user interface toolkits like Tk.
Python 可以让你把自己的程序分隔成不同的模块，以便在其它的 Python 程序 中重用。这样你就可以让自己的程序基于一个很大的标准模块集或者用它们做为 示例来学习 Python 编程。Python 中集成了一些类似文件 I/O，系统调 用，sockets，甚至像 Tk 这样的图形工具接口。
Python is an interpreted language, which can save you considerable time during program development because no compilation and linking is necessary. The interpreter can be used interactively, which makes it easy to experiment with features of the language, to write throw-away programs, or to test functions during bottom-up program development. It is also a handy desk calculator.
Python是一门解释型语言，因为不需要编译和链接的时间，它可以帮你省下一些 开发时间。解释器可以交互式使用，这样就可以很方便的测试语言中的各种功 能，以便于编写发布用的程序，或者进行自下而上的开发。还可以当它是一个随 手可用的计算器。
Python enables programs to be written compactly and readably. Programs written in Python are typically much shorter than equivalent C, C++, or Java programs, for several reasons:
Python 可以写出很紧凑和可读性很强的程序。用 Python 写的程序通常比同样 的 C、C++ 或Java程序要短得多，这是因为以下几个原因：
* the high-level data types allow you to express complex operations in a single statement;
* statement grouping is done by indentation instead of beginning and ending brackets;
* no variable or argument declarations are necessary.
* 高级数据结构使你可以在一个单独的语句中表达出很复杂的操作；
* 语句的组织依赖于缩进而不是 begin/end 块；
* 不需要变量或参数声明。
Python is *extensible*: if you know how to program in C it is easy to add a new built-in function or module to the interpreter, either to perform critical operations at maximum speed, or to link Python programs to libraries that may only be available in binary form (such as a vendor-specific graphics library). Once you are really hooked, you can link the Python interpreter into an application written in C and use it as an extension or command language for that application.
Python 是 可扩展的：如果你会用 C 语言写程序，那就可以很容易的为解释器 添加新的集成模块和功能，或者优化瓶颈，使其达到最大速度，或者使 Python 能够链接到所需的二进制架构上（比如某个专用的商业图形库）。等你真正熟悉 这一切了，你就可以将 Python 集成进由 C 写成的程序，把 Python 当做这个 程序的扩展或命令行语言。
By the way, the language is named after the BBC show "Monty Python's Flying Circus" and has nothing to do with reptiles. Making references to Monty Python skits in documentation is not only allowed, it is encouraged!
顺便说一下，这个语言的名字来源于 BBC 的“Monty Python's Flying Circus”节目，和凶猛的爬虫没有任何关系。在文档中引用 Monty Python 典故 不仅可以，而且还很恰当！
Now that you are all excited about Python, you'll want to examine it in some more detail. Since the best way to learn a language is to use it, the tutorial invites you to play with the Python interpreter as you read.
现在我们已经了解了 Python 中所有激动人心的东西，大概你想仔细的试试它了。 学习一门语言最好的办法就是使用它，如你所读到的，本文会引领你运用 Python 解释器。
In the next chapter, the mechanics of using the interpreter are explained. This is rather mundane information, but essential for trying out the examples shown later.
下一节中，我们直接说明解释器的用法。这没有什么神秘的内容，不过有助于我 们练习后面展示的例子。
The rest of the tutorial introduces various features of the Python language and system through examples, beginning with simple expressions, statements and data types, through functions and modules, and finally touching upon advanced concepts like exceptions and user-defined classes.
本指南其它部分通过例子介绍了 Python 语言和系统的各种功能，开始是简单表 达式、语法和数据类型，接下来是函数和模块，最后是诸如异常和自定义类这样 的高级内容。
********************************* Whetting Your Appetite 开胃菜 *********************************
If you do much work on computers, eventually you find that there's some task you'd like to automate. For example, you may wish to perform a search-and-replace over a large number of text files, or rename and rearrange a bunch of photo files in a complicated way. Perhaps you'd like to write a small custom database, or a specialized GUI application, or a simple game.
如果你要在计算机上做大量的工作，希望它们能够自动化一些。例如，你想在大 量的文本文件中进行查找替换，或者通过复杂的方式将一批图像文件重命名，修 改尺寸。可能你想写一个小型的定制数据库，或者特定的 GUI 应用程序，或者 一个简单的游戏。
If you're a professional software developer, you may have to work with several C/C++/Java libraries but find the usual write/compile/test/re-compile cycle is too slow. Perhaps you're writing a test suite for such a library and find writing the testing code a tedious task. Or maybe you've written a program that could use an extension language, and you don't want to design and implement a whole new language for your application.
如果你是专业的软件开发者，可能会想使用一些 C/C++/Java 库，但是发现通常 的编写/编译/测试/重编译循环太慢了。也许你想为每个写一个测试，可这样做 太麻烦。或者你需要写一个带有扩展语言的程序，可不想为你的应用程序设计和 实现一个新的语言。
Python is just the language for you.
Python 就是你需要的语言。
You could write a Unix shell script or Windows batch files for some of these tasks, but shell scripts are best at moving around files and changing text data, not well-suited for GUI applications or games. You could write a C/C++/Java program, but it can take a lot of development time to get even a first-draft program. Python is simpler to use, available on Windows, Mac OS X, and Unix operating systems, and will help you get the job done more quickly.
你也可以写一个 Unix shell 脚本或者 Windows 批处理文件完成任务，不过 shell 脚本最擅长移动文件和修改文本数据，不擅长编写图形界面的应用程序或 游戏。你可以写个 C/C++/Java 程序，但是就算也一个最简单的草案，也要花 费太多的开发时间。 Python 更易用，并且在 Windows， Mac OS X 和 Unix 操 作系统上可用，能够帮你更快的完成任务。
Python is simple to use, but it is a real programming language, offering much more structure and support for large programs than shell scripts or batch files can offer. On the other hand, Python also offers much more error checking than C, and, being a *very-high-level language*, it has high-level data types built in, such as flexible arrays and dictionaries. Because of its more general data types Python is applicable to a much larger problem domain than Awk or even Perl, yet many things are at least as easy in Python as in those languages.
Python 简单易用，但它是真正的编程语言，比起 shell 脚本或批处理文件，可 以提供更多对大型程序的构造和支持。另一方面，Python 比起C，提供更多的错 误检查。而且作为 *非常高级的编程语言* ，它内置了类似变长数组和字典这样 的高级数据结构。Python 提供了更为通用的数据类型，所以它比 Awk 甚至 Perl 适合更广大的问题领域，做其它的很多事，Python 至少也不会比别的编程语言更复杂。
Python allows you to split your program into modules that can be reused in other Python programs. It comes with a large collection of standard modules that you can use as the basis of your programs --- or as examples to start learning to program in Python. Some of these modules provide things like file I/O, system calls, sockets, and even interfaces to graphical user interface toolkits like Tk.
Python 可以让你把自己的程序分隔成不同的模块，以便在其它的 Python 程序 中重用。这样你就可以让自己的程序基于一个很大的标准模块集或者用它们做为 示例来学习 Python 编程。Python 中集成了一些类似文件 I/O，系统调 用，sockets，甚至像 Tk 这样的图形工具接口。
Python is an interpreted language, which can save you considerable time during program development because no compilation and linking is necessary. The interpreter can be used interactively, which makes it easy to experiment with features of the language, to write throw-away programs, or to test functions during bottom-up program development. It is also a handy desk calculator.
Python是一门解释型语言，因为不需要编译和链接的时间，它可以帮你省下一些 开发时间。解释器可以交互式使用，这样就可以很方便的测试语言中的各种功 能，以便于编写发布用的程序，或者进行自下而上的开发。还可以当它是一个随 手可用的计算器。
Python enables programs to be written compactly and readably. Programs written in Python are typically much shorter than equivalent C, C++, or Java programs, for several reasons:
Python 可以写出很紧凑和可读性很强的程序。用 Python 写的程序通常比同样 的 C、C++ 或Java程序要短得多，这是因为以下几个原因：
* the high-level data types allow you to express complex operations in a single statement;
* statement grouping is done by indentation instead of beginning and ending brackets;
* no variable or argument declarations are necessary.
* 高级数据结构使你可以在一个单独的语句中表达出很复杂的操作；
* 语句的组织依赖于缩进而不是 begin/end 块；
* 不需要变量或参数声明。
Python is *extensible*: if you know how to program in C it is easy to add a new built-in function or module to the interpreter, either to perform critical operations at maximum speed, or to link Python programs to libraries that may only be available in binary form (such as a vendor-specific graphics library). Once you are really hooked, you can link the Python interpreter into an application written in C and use it as an extension or command language for that application.
Python 是 可扩展的：如果你会用 C 语言写程序，那就可以很容易的为解释器 添加新的集成模块和功能，或者优化瓶颈，使其达到最大速度，或者使 Python 能够链接到所需的二进制架构上（比如某个专用的商业图形库）。等你真正熟悉 这一切了，你就可以将 Python 集成进由 C 写成的程序，把 Python 当做这个 程序的扩展或命令行语言。
By the way, the language is named after the BBC show "Monty Python's Flying Circus" and has nothing to do with reptiles. Making references to Monty Python skits in documentation is not only allowed, it is encouraged!
顺便说一下，这个语言的名字来源于 BBC 的“Monty Python's Flying Circus”节目，和凶猛的爬虫没有任何关系。在文档中引用 Monty Python 典故 不仅可以，而且还很恰当！
Now that you are all excited about Python, you'll want to examine it in some more detail. Since the best way to learn a language is to use it, the tutorial invites you to play with the Python interpreter as you read.
现在我们已经了解了 Python 中所有激动人心的东西，大概你想仔细的试试它了。 学习一门语言最好的办法就是使用它，如你所读到的，本文会引领你运用 Python 解释器。
In the next chapter, the mechanics of using the interpreter are explained. This is rather mundane information, but essential for trying out the examples shown later.
下一节中，我们直接说明解释器的用法。这没有什么神秘的内容，不过有助于我 们练习后面展示的例子。
The rest of the tutorial introduces various features of the Python language and system through examples, beginning with simple expressions, statements and data types, through functions and modules, and finally touching upon advanced concepts like exceptions and user-defined classes.
本指南其它部分通过例子介绍了 Python 语言和系统的各种功能，开始是简单表 达式、语法和数据类型，接下来是函数和模块，最后是诸如异常和自定义类这样 的高级内容。
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