Python 官方简明教程 1

— 1. 能令您兴趣盎然的Python（正在翻译中）

如果您长期在电脑前工作，您也许会希望让某些工作能在电脑上自动完成。例如，在一大堆文本文件里查找和替换某个词语，或者给一批照片重新排序并重命名，又也许您想写一个小型的自定义数据库，或者写一个专用的GUI应用，甚至写一个简单的游戏。

如果您是一个专业的软件开发人员，可能在您不得不使用C/C++/Java库工作时就已经发现，通常“写代码、编译、测试、再编译”这样循环工作的效率太低了，也许您正在为这样的库测试套件和测试代码进行着枯燥乏味的编写任务，或者也许您已经写了一个可以使用扩展语言的程序，然而您却不打算为您的应用程序设计并实施一整套全新的程序语言。

Python正好就是您需要的编程语言。

你可以通过写一个Unix的shell脚本或者Windows的批处理文件来完成一些工作，但shell脚本只擅长于搬弄文件和修改文本数据，并适用于GUI应用和游戏开发。您可以写一个C/C++/Java程序，但它会耗费大量的开发时间却甚至只完成了第一程序的草稿。Python简单易用，兼容于Windows， Mac OS X，和Unix操作系统，将能帮助您更迅速地完成工作。

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 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 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 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:

• 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.

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.

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!

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.

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.

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.

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