Python编程入门与实践指南

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"Making Use of Python (2002)" 是一本由Rashi Gupta编著，Wiley Publishing出版的Python编程教程。这本书旨在帮助初学者理解并掌握Python语言的基础知识和核心概念。书籍中涵盖了从安装Python、编写第一个程序到更高级的主题，如函数、模块、面向对象编程和异常处理等。以下是各个章节的关键知识点： 1. **简介**: 提供了关于Python的基本介绍，解释了为什么选择Python以及如何开始学习Python。 2. **开始Python之旅**: 阐述了如何获取Python环境，理解需求，安装Python，并在不同模式下运行Python解释器。 3. **Python入门**: 介绍了如何写第一个Python程序，包括注释、变量、基本数据类型（如整数、浮点数和字符串）以及内存管理。 4. **内置操作与输入/输出**: 讲解了如何使用Python的输入/输出功能，接受用户输入，格式化输出，以及针对不同类型数据的内置操作。 5. **编程基础**: 深入讨论了条件语句（如if-else）、运算符优先级，以及使用控制流和循环结构。 6. **函数**: 解释了函数的定义、调用和作用域，包括局部和全局变量的概念。 7. **模块**: 介绍了如何组织代码，使用模块和包来实现代码重用和结构化项目。 8. **文件操作**: 教授如何与文件交互，读写文件，存储和读取数据。 9. **面向对象编程**: 引入了面向对象编程的基本概念，如类、对象、继承和方法覆盖。 10. **异常处理**: 讨论了错误和异常处理，包括识别错误类型、捕获异常以及编写异常处理代码。 11. **CGI编程**: 介绍了如何编写CGI（Common Gateway Interface）应用程序，以实现服务器端脚本，创建动态网页。 12. **数据库编程**: 简述了数据库管理，特别是MySQL的使用，以及如何从Python脚本访问和操作数据库。本书不仅适合初学者，也适合有一定经验的程序员，作为Python学习和进阶的参考。通过书中丰富的示例和实践练习，读者可以逐步掌握Python编程的核心技能。

... print 1+1

Alternatively, you can write a program in a file and use the interpreter to execute the

contents of the file. Such a file written in Python is called a script. For example, a text

editor can be used to write a file, calculate.py, with the following contents:

print 1 + 1

By convention, files that contain Python programs have names with the .py extension.

To execute the program, you need to specify the name of the script at the interpreter.

$ python calculate.py

Extensible and Flexible

An application that contains a large amount of code can be effectively organized into

smaller modules due to Python’s dual structured and object-oriented programming

environments. These modules can still interact with each other or with other built-in

modules. Python’s syntax is the same for accessing both the user-defined and the built-

in standard modules. Python is also extremely flexible in the treatment of language

components. For example, a Python module that is meant to interact with the external

environment can be tested using an imitation of the external environment written in

Python.

Rich Core Library

Many development modules are built into Python and are part of the Python Standard

Library. A programmer can make use of these tools in the Python Standard Library,

depending on the application for which the tools are required. Besides modules that

work on all platforms, the library has modules that are specific to a particular platform

or environment. Python standard modules perform all types of usual tasks, such as

HTTP, FTP, POP, SMTP, and many other services. Using the rich core library, you can

write applications for downloading a Web page, parsing HTML files, developing a

graphic user interface (GUI), and so on.

Memory Management

C and C++ programmers always need to write code for handling memory manage-

ment and memory modification even if the program has very little to do with memory

access. This always results in an extra burden on the programmer. One clear example

is the need for tracking each object and deleting the reserved memory once the object

ends its life. This is the responsibility of the developer, and any failure can lead to

Introduction xv

memory leaks and other negative consequences. In Python, the interpreter manages

memory, thus removing the extra burden on the programmer. This results in fewer

errors and a more efficient application involving less development time.

Web Scripting Support and Data Handling

Python is popularly used for developing Internet and intranet applications. Python is

well suited for Internet and intranet applications because these applications are highly

dynamic and complex, and at times, they need to interact with several environments.

Python’s dynamism, the ease with which you can write complex applications, and its

advanced features, such as HTML, XML, and SGML parsing, allow you to write CGI

scripts for several environments.

Object Distribution

You can use Python to implement routines that can communicate with objects in other

languages. For example, Python can be used to pass data to COM components. In

addition, Common Object Request Broker Architecture (CORBA) can be implemented

in Python as well, which enables you to use cross-platform distributed objects.

Databases

Python provides interfaces to all major commercial databases. Besides that, it has built-

in modules that enable you to handle flat file databases. It also has object persistence

systems that can write entire objects to files. Python’s most important database-

programming feature, though, is Python API. This API includes functions that make it

easy to write applications that communicate with different databases.

GUI Programming

Python supports GUI applications that can be created and ported to many system calls,

libraries, and windows systems, such as Windows MFC, Macintosh, and the X Window

system of Unix. This is possible using Python’s default graphic user interface library,

Tkinter. Tkinter is the standard object-oriented interface of the TK GUI API, which is

the official GUI development platform of Python.

Extendable and Embeddable

You can add low-level modules to the Python interpreter. These modules enable pro-

grammers to add to or customize their tools to be more efficient. Compiled extension

modules can be created in Python to connect Python modules with external program-

ming libraries or new data types. Extension modules are easily created and maintained

using Python. Most platforms support the loading of new compiled components into

the interpreter dynamically. Python extension modules can be written in C and C++ for

CPython and in Java for JPython.

xvi Introduction

The Python interpreter can be embedded into another programming or scripting

application. Any other program can use the Python interpreter as a simple application

program interface (API). Therefore, the Python interpreter can act as a scripting tool

that glues everything.

Exception Handling

When running a program, if Python exits due to an error, it generates a complete stack

trace of errors. This stack trace indicates the name and type of the error that occurred.

The exception handling in Python allows you to detect errors at run time without adding

error-checking statements to your code. Exception handlers can be written in Python to

defuse a problem, perform a clean-up or maintenance action, or redirect the program

flow. This allows a programmer to put in considerably less effort to debug an error.

Portable

Python can run on a wide variety of hardware platforms and has the same interface on

all platforms. Its design is not linked to a particular operating system because it is writ-

ten in portable ANSI C. This means that you can write, test, and upload a program

written in Python on Windows, Linux, and Macintosh environments. This depends on

whether the application is developed to implement specific commands of an operating

system or if the application uses modules that do not work on all platforms. In these

situations, the application cannot run on all hardware platforms; however, this affects

only a few modules. Usually, the applications that you create run on all the platforms

without changing any code.

Freeware

Python is freeware and can be redistributed freely in the source form. The copyright of

Python does not allow authors to place it at risk legally and does prevent users from

hijacking its copyright. Programmers and users are allowed to use Python’s source in

any desired way. Programmers can create applications and release them in the binary-

only form, which has modules in only the byte-compiled form. The result of the prod-

uct can, however, be sold or distributed in any manner.

Users and Application Areas of Python

Python is an advanced scripting language that is being used in various areas. Some of

the areas where Python is being used are the following:

■■

Gluing together large software components. These large software components

can be written in C, C++, or Java.

■■

Creating prototypes of an application. The prototype can be written in Python

without writing any C, C++, or Java code. Often, the prototype is sufficiently

functional and performs well enough to be delivered as the final product, sav-

ing considerable development time.

Introduction xvii

■■

Writing CGI scripts on all platforms (Unix, Windows, and Mac). Because of this

ability Python has a strong presence on the Web.

Besides these, Python is also well represented in the distributed systems world. It is

one of the main languages supported by Xerox PARC’s ILU. It has also been used to

implement the Web browser Grail.

A list of Python users worldwide include the following:

■■

NASA

■■

Infoseek

■■

Digital Creations

■■

Grail

■■

Xerox

■■

Hewlett-Packard

■■

CMU

■■

Digital Media Inc.

■■

University of Queensland, Australia

■■

Space Telescope Science Institute

■■

Mind Spring

■■

Mitretek Systems

Python versus Other Languages

It is a well-known fact that scripting languages are slower than compiled languages.

The Python interpreter carries out most of the tasks that are carried out by a compiler

in all compiled languages. at Python, however, is an intermediate language that pro-

vides the features of both compiled and interpreted languages. Python can be com-

pared with many other languages mainly because it provides many salient features in

other languages and is derived from many languages, such as C, C++, Modula-3, ABC,

SmallTalk, and Unix shell.

Python is often compared with C and C++ because it has syntax similar to the syn-

tax of these languages. Python is considered a good tool to test C and C++ applications.

It also glues some components of C/C++ contributing to C/C++ projects. In many

ways, Python has merits over C/C++. Memory allocation and reference errors that

occur in C/C++ are eliminated by the Python interpreter, which performs automatic

memory management. Python code is usually easier and smaller than that in C and

C++. Python’s array constructs generate fewer problems than the array constructs of

C and C++.

Perl is another scripting language that you can compare with Python. Like Python,

Perl is of great use to programmers and system administrators. Perl is also a powerful

language for text manipulation and data extraction. Unlike Python, though, Perl has a

difficult syntax that dissuades beginners from learning it. Perl is a popular language

xviii Introduction

used to develop Common Gateway Interface (CGI) scripts for Internet programming.

Programmers working on the same large project find it difficult to understand each

other’s code because there are many ways of writing a program.

Tcl is also one of the popular scripting languages. Python is compared with Tcl for

many reasons. Tcl is a powerful and easy scripting language that provides the features

of a programming language as well as tools for system calls. Tcl is a more restrictive

language than Python because it has fewer data types than Python. Python uses the

same toolkit, Tk, as Tcl for developing GUI applications.

Python uses the OOP concept and has syntax similar to that of Java. Unlike Python,

Java applications require huge code and a compilation phase. Moreover, Python offers

dynamic typing and a rapid development environment. Python, though, is slower and

less portable than Java. A breakthrough in the relationship of Python and Java is

JPython, a Python interpreter that is constructed completely in Java. It can run on any

machine containing Java Virtual Machine (JVM). It provides programmers with the

features of Python along with a hoard of Java classes. A complete discussion on

JPython is out of the scope of this book. Some of its salient features are as follows:

■■

JPython provides a scripting environment for Java development.

■■

JPython generates a truly object-oriented programming environment.

■■

An application written in JPython can access Java classes directly and can inte-

grate them with its own JPython classes, whenever required.

■■

JPython provides access to Java AWT/Swing libraries for GUI development.

■■

Compiled JPython programs create Java byte code, creating a .class file,

which can be used to create applets.

How This Book Is Organized

This book shrugs away from the traditional content-based approach and uses the

problem-based approach to present the concepts of Python. Problems used in the book

are presented against the backdrop of real-life scenarios. The problem is followed by a

task list that helps to solve that problem, in the process delivering the concepts and

their implementation. This practical approach will help readers to understand the real-

life application of the language and its use in various scenarios. Moreover, to provide

an appropriate learning experience, the concepts will be supported adequately by case

studies that will be formulated in such a way that they provide a frame of reference for

the reader.

Chapter 1 is a guide to obtaining the Python software and its documentation. It also

discusses installation of Python on Unix, Linux, and Windows systems. Finally. it dis-

cusses the execution modes of Python and starting Python in Unix, Linux, and Windows.

Chapter 2 is a getting-started guide. It leads into developing a simple Python

program. Then, it discusses the standard data types, type operators, and expressions.

Finally, it mentions the identifiers and keywords in Python.

Introduction xix

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