Python编程入门：从零开始掌握编程基础

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"Learning To Program Using Python - Cody Jackson (2009)" 本书"Learning To Program Using Python"是针对编程初学者的一本理想入门教材，它通过Python语言帮助读者逐步理解编程的基础概念，并逐渐深入到面向过程和面向对象的编程思想。作者Cody Jackson在2009年创作了这本书，旨在提供一个友好的学习路径，让初学者能够轻松踏入编程世界。书中的内容可能涵盖以下几个关键知识点： 1. **Python基础知识**：Python是一种高级编程语言，以其简洁的语法和强大的功能而闻名。初学者会学习到基本的数据类型（如整数、浮点数、字符串和布尔值），变量的声明和赋值，以及控制流程结构（如条件语句和循环）。 2. **面向过程编程**：这是一种编程范式，强调通过过程或步骤来解决问题。初学者会了解到如何组织和编写函数，以实现模块化的代码，提高程序的可读性和可维护性。 3. **面向对象编程（OOP）**：Python支持面向对象编程，这是另一种重要的编程范式，允许我们通过创建和操作对象来设计复杂的程序。OOP的核心概念包括类（class）、对象（object）、继承（inheritance）、封装（encapsulation）和多态性（polymorphism）。 4. **数据结构**：Python提供了丰富的内置数据结构，如列表（list）、元组（tuple）、字典（dictionary）和集合（set）。理解并熟练使用这些数据结构对于编写高效代码至关重要。 5. **函数和模块**：学习如何定义和调用函数，以及如何将相关功能组织成模块，有助于代码的重用和代码结构的清晰。 6. **异常处理**：了解如何使用try/except语句来捕获和处理程序运行时可能出现的错误，是编写健壮代码的关键。 7. **文件操作**：学习如何读写文件，这是任何程序员都需要掌握的基本技能。 8. **调试和测试**：介绍如何使用调试工具和编写测试用例来查找和修复代码中的错误，确保程序的正确性。 9. **版本控制**：可能会提及使用Git等版本控制系统的重要性，这对于协作开发和项目管理非常关键。 10. **Python标准库**：介绍Python自带的一些常用库，如os、sys、math等，以及如何利用它们扩展程序的功能。此外，书籍的开源性质意味着读者还可以接触到开源软件的许可证，例如GNU Free Documentation License和GNUGeneral Public License。这些许可证允许自由地复制、分发和修改文档或代码，但同时也规定了一些使用和修改的条款，比如必须保留原始作者的版权信息和许可条款。 "Learning To Program Using Python"是一本全面且实用的教材，适合想要学习编程的新手，它不仅教授Python语言本身，还涵盖了编程思维和实践中的重要原则。通过学习这本书，初学者可以建立起坚实的编程基础，并具备进一步探索更复杂编程概念的能力。

CHAPTER 3. COMPARISON OF PROGRAMMING LANGUAGES 15

3.5 Python

#! / u sr / bin / env python

# −∗− c od in g : is o −8859−1 −∗−

"""

99 B o t t l e s o f Beer ( by Gerold Penz )

Python can be s imp le , to o : − )

"""

for quant in range (99 , 0 , − 1):

i f quant > 1 :

print quant , " b o t t l e s o f beer on the wall , " , quant , " b o t t l e s o f beer . "

i f quant > 2 :

s u f f i x = s t r ( quant − 1) + " b o t t l e s o f beer on the wall . "

el se :

s u f f i x = "1 b o t t l e o f beer on the w all . "

e l i f quant == 1 :

print "1 b o t t l e o f beer on the wall , 1 b o t t l e o f beer . "

s u f f i x = "no more be er on the wall ! "

print "Take one down , pass i t around , " , s u f f i x

print "−−"

CHAPTER 4. THE PYTHON INTERPRETER 17

Listing 4.1: Example Python interpreter

Python 2 . 5 . 1 ( r251 : 5 4 8 63 , Jan 17 2008 , 1 9 : 3 5 : 1 7 )

[GCC 4 . 0 . 1 ( Apple Inc . b u i l d 5 4 6 5) ] on darwin

Type " h elp " , " c o pyri g h t " , " c r e d i t s " or " l i c e n s e " for more i nfor m a t i on .

>>>

You may notice that the Python version used in the above examples is 2.5.1; the current version is 3.0.

Don’t panic. The vast majority of what you will learn will work regardless of what version you’re using. My

favorite Python book, Python How to Program, is based on version 2.2 but I still use it nearly every day as

a reference while coding.

For the most part, you won’t even notice what version is in use, unless you are using a library, function,

or method for a speciﬁc version. Then, you simply add a checker to your code to identify what version the

user has and notify him to upgrade or modify your code so it is backwards-compatible.

(A later chapter in this book will cover all the major diﬀerences you need to be aware of when using

Python 3. Right now you’re just learning the basics that you will use regardless of which version of the

language you end up using.)

The >>> in Listing 4.1 is the Python command prompt; your code is typed here and the result is

printed on the following line, without a prompt. For example, Listing 4.2 shows a simple print statement

from Python 2.5:

Listing 4.2: Python command prompt

>>>print "We a re the kni g h ts who say , ’ Ni ’ . "

We are the k n i ghts who say , ’ Ni ’ .

4.2 Python Versions

As an aside, Python 3 has changed print from a simple statement, like Listing 4.2, into a bona-ﬁde function

(Listing 4.3). Since we haven’t talked about functions yet, all you need to know is that Python 3 simply

requires you to use the print statement in a slightly diﬀerent way: parenthesis need to surround the quoted

words. Just so you’re aware.

Listing 4.3: Print function (Python 3)

>>>print ( "We a re the kni g h t s who say , ’ Ni ’ . " )

We are the k n i ghts who say , ’ Ni ’ .

The vast majority of the code in this book will be written for Python 2.6 or earlier, since those versions

are installed by default on many *nix systems and is therefore still very popular; there is also a lot of older

code in the wild, especially open-source programs, that haven’t been (and probably never will be) upgraded

to Python 3. If you decide to use other Python programs to study from or use, you will need to know the

“old school” way of Python programming; many open-source programs are still written for Python 2.4.

If you are using Python 3 and you want to type every example into your computer as we go along, please

be aware that the print statements, as written, won’t work. They will have to be modiﬁed to use a print()

function like in Listing 4.3.

4.3 Using the Python Command Prompt

If you write a statement that doesn’t require any “processing” by Python, it will simply return you to the

prompt, awaiting your next order. The next code example shows the user assigning the value “spam” to the

variable can. Python doesn’t have to do anything with this, in regards to calculations or anything, so it

accepts the statement and then waits for a new statement.

Listing 4.4: Python statements

>>>can = "spam"

>>>

CHAPTER 4. THE PYTHON INTERPRETER 18

(By the way, Python was named after Monty Python, not the snake. Hence, much of the code you’ll ﬁnd

on the Internet, tutorials, and books will have references to Monty Python sketches.)

The standard Python interpreter can be used to test ideas before you put them in your code. This is a

good way to hash out the logic required to make a particular function work correctly or see how a conditional

loop will work. You can also use the interpreter as a simple calculator. This may sound geeky, but I often

launch a Python session for use as a calculator because it’s often faster than clicking through Windows’

menus to use its calculator.

Here’s an example of the “calculator” capabilities:

Listing 4.5: Python as a calculator

>>>2+2

>>>4∗4

>>>5∗∗2

Python also has a math library that you can import to do trigonometric functions and many other higher

math calculations. Importing libraries will be covered later in this book.

4.4 Commenting Python

One ﬁnal thing to discuss is that comments in Python are marked with the “#” symbol. Comments are used

to annotate notes or other information without having Python try to perform an operation on them. For

example,

Listing 4.6: Python comments

>>>d i c t = {" F i r s t p hon eti c " : " Able " , "Second p hon e tic " : " Backer "} #c r e a t e a d i c t i o n a r y

>>>print d i c t . keys ( ) #n o t i c e t h a t d i c t i o n a r y v a l u e s aren ’ t k e p t i n o rd er

[ ’ Second ph one t ic ’ , ’ F i r s t p hon e tic ’ ]

>>>print d i c t [ " F i r s t p hon eti c " ] #p r i n t t h e v a lue a s s o c i a t e d w it h t h e key

Able

You will see later on that, even though Python is a very readable language, it still helps to put comments

in your code. Sometimes it’s to explicitly state what the code is doing, to explain a neat shortcut you used,

or to simply remind yourself of something while you’re coding, like a “todo” list.

4.5 Launching Python programs

If you want to run a Python program, simply type python at the shell command prompt (not the IDE)

followed by the program name.

Listing 4.7: Launching a Python program

$python f oo . py

Files saved with the .py extension are called modules and can be called individually at the command

line or within a program, similar to header ﬁles in other languages. If your program is going to import

other modules, you will need to make sure they are all saved in the same directory on the computer. More

information on working with modules can be found later in this book or in the Python documentation.

Depending on the program, certain arguments can be added to the command line when launching the

program. This is similar to adding switches to a Windows DOS prompt command. The arguments tell the

program what exactly it should do. For example, perhaps you have a Python program that can output it’s

processed data to a ﬁle rather than to the screen. To invoke this function in the program you simply launch

the program like so:

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