Python 3.1+入门教程：实战与方法

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"Hands-on Python Tutorial" 是一份针对Python 3.1+版本的实用指南，由Andrew N. Harrington博士编著，适用于Loyola University Chicago。这份教程旨在提供一个实践导向的学习体验，适合初学者逐步掌握Python语言的基础知识和核心概念。教程的第一部分从“开始使用Python”开始，引导读者了解编程环境，包括Python解释器和IDLE（集成开发环境）的使用。接着深入探讨了Python的数据类型和函数，如整数运算、字符串处理、变量赋值以及打印功能。这部分内容强调了通过实践操作来理解基本概念的重要性。在第二部分，对象和方法成为关注焦点。字符串的进一步探讨，类和方法的创建，以及MadLibs游戏的重新实现，展示了如何利用Python进行文本处理和图形处理。此外，教程还涵盖了文件操作，让学习者了解如何在程序中读写文件。第三部分深入讲解了控制流，包括条件语句、循环结构（如for和while循环）以及如何处理不同类型的数据作为布尔值。这部分内容有助于读者理解如何灵活地控制程序的执行流程。最后，第四部分转向动态网页开发，为那些对Web开发感兴趣的学习者提供了概述，包括网页基础、网页构成以及如何利用Python构建基本的Web页面。这部分内容展示了Python在实际应用中的实用性，特别是与Web技术的结合。整个教程以实践为主，每个章节都包含丰富的实例和练习，使读者能够在动手操作中不断巩固所学知识。无论是初次接触Python的新手，还是希望提升技能的进阶者，这份教程都是一个极具价值的学习资源。

Hands-on Python Tutorial, Release 1.0 for Python Version 3.1+

6+3

Be sure to end with the Enter key. After the Shell responds, you should see something like

>>> 6+3

>>>

The shell evaluates the line you entered, and prints the result. You see Python does arithmetic. At the end you see a

further prompt >>> where you can enter your next line.... The result line, showing 9, that is produced by the computer,

does not start with >>>.

1.3 Whirlwind Introduction To Types and Functions

Python directly recognizes a variety of types of data. Here are a few:

Numbers: 3, 6, -7, 1.25

Character strings: ’hello’, ’The answer is: ’

Lists of objects of any type: [1, 2, 3, 4], [’yes’, ’no’, ’maybe’]

A special datum meaning nothing: None

Python has large collection of built-in functions that operate on different kinds of data to produce all kinds of results.

To make a function do its action, parentheses are required. These parentheses surround the parameter or parameters,

as in a function in algebra class.

The general syntax to execute a function is

functionName ( parameters )

One function is called type, and it returns the type of any object. The Python Shell will evaluate functions. In the

Shell the last line should look like

>>>

Continuing on the same line enter

12 Chapter 1. Beginning With Python

Hands-on Python Tutorial, Release 1.0 for Python Version 3.1+

type(7)

Always remember to end with the Enter key. After the Shell responds, you should see something like

>>> type(7)

>>>

In the result, int is short for integer. The word class is basically a synonym for type in Python.

Note that the line with the value produced by the shell does not start with >>> and appears at the left margin. Hence

you can distinguish what you type (after the >>> prompt) from what the computer responds.

At the end you see a further prompt where you can enter your next line....

For the rest of this section, at the >>> prompt in the Python Shell, individually enter each line below that is set off in

typewriter font. So next enter

type(1.25)

Note the name in the last result is float, not real or decimal, coming from the term “ﬂoating point”, for reasons that

will be explained later, in Floats, Division, Mixed Types (page 59).

Enter

type(’hello’)

In your last result you see another abbreviation: str rather than string. Enter

type([1, 2, 3])

Strings and lists are both sequences of parts (characters or elements). We can ﬁnd the length of that sequence with

another function with the abbreviated name len. Try both of the following, separately, in the Shell:

len([2, 4, 6])

len(’abcd’)

Some functions have no parameters, so nothing goes between the parentheses. For example, some types serve as

no-parameter functions to create a simple value of their type. Try

list()

You see the way an empty list is displayed.

Functions may also take more than one parameter. Try

max(5, 11, 2)

Above, max is short for maximum.

Some of the names of types serve as conversion functions (where there is an obvious meaning for the conversion). Try

each of the following, one at a time, in the Shell:

str(23)

int(’125’)

An often handy Shell feature: an earlier Shell line may to copied and edited by clicking anywhere in the previously

displayed line and then pressing the Enter key. For instance you should have entered several lines starting with len.

click on any one, press Enter, and edit the line for a different test.

1.3. Whirlwind Introduction To Types and Functions 13

Hands-on Python Tutorial, Release 1.0 for Python Version 3.1+

1.4 Integer Arithmetic

1.4.1 Addition and Subtraction

We start with the integers and integer arithmetic, not because arithmetic is exciting, but because the symbolism should

be mostly familiar. Of course arithmetic is important in many cases, but Python is probably more often used to

manipulate text and other sorts of data, as in the sample program in ref:Running-A-Sample.

Python understands numbers and standard arithmetic. For the whole section on integer arithmetic, where you see a

set-off line in typewriter font, type individual lines at the >>> prompt in the Python Shell. Press Enter after each

line to get Python to respond:

2 + 3

5 - 7

Python should evaluate and print back the value of each expression. Of course the ﬁrst one does not require any

calculation. It appears that the shell just echoes back what you printed.

The Python Shell is an interactive interpreter. As you can see, after you press Enter, it is evaluating the expression

you typed in, and then printing the result automatically. This is a very handy environment to check out simple Python

syntax and get instant feedback. For more elaborate programs that you want to save, we will switch to an Editor

Window later.

1.4.2 Multiplication, Parentheses, and Precedence

Try in the Shell:

2 x 3

You should get your ﬁrst syntax error. The x should have become highlighted, indicating the location where the Python

interpreter discovered that it cannot understand you: Python does not use x for multiplication as you may have done

in grade school. The x can be confused with the use of x as a variable (more on that later).

Instead the symbol for multiplication is an asterisk

. Enter each of the following. You may include spaces or not.

The Python interpreter can ﬁgure out what you mean either way. Try in the Shell:

2 + 3

If you expected the last answer to be 20, think again: Python uses the normal precedence of arithmetic operations:

Multiplications and divisions are done before addition and subtraction, unless there are parentheses. Try

(2+3)

(4 - 1)

Now try the following in the Shell, exactly as written, followed by Enter, with no closing parenthesis:

(2 + 3

Look carefully. There is no answer given at the left margin of the next line and no prompt >>> to start a new expression.

If you are using Idle, the cursor has gone to the next line and has only indented slightly. Python is waiting for you to

ﬁnish your expression. It is smart enough to know that opening parentheses are always followed by the same number

of closing parentheses. The cursor is on a continuation line. Type just the matching close-parenthesis and Enter,

)

14 Chapter 1. Beginning With Python

Hands-on Python Tutorial, Release 1.0 for Python Version 3.1+

Having the choice of delimiters can be handy.

Figure out how to give Python the string containing the text: I’m happy. Try it. If you got an error, try it with

another type of quotes, and ﬁgure out why that one works and not the ﬁrst.

There are many variations on delimiting strings and embedding special symbols. We will consider more ways later in

Strings Part II (page 20).

Note: A string can have any number of characters in it, including 0. The empty string is ’’ (two quote characters

with nothing between them). Many beginners forget that having no characters is legal. It can be useful.

Strings are a new Python type. Try

type(’dog’)

type(’7’)

type(7)

The last two lines show how easily you can get confused! Strings can include any characters, including digits. Quotes

turn even digits into strings. This will have consequences in the next section....

1.5.2 String Concatenation

Strings also have operation symbols. Try in the Shell (noting the space after very):

’very ’ + ’hot’

The plus operation with strings means concatenate the strings. Python looks at the type of operands before deciding

what operation is associated with the +.

Think of the relation of addition and multiplication of integers, and then guess the meaning of

’very ’ + ’hot’

Were you right? The ability to repeat yourself easily can be handy.

Predict the following and then test. Remember the last section on types:

7+2

’7’+’2’

Python checks the types and interprets the plus symbol based on the type. Try

’7’+2

With mixed string and int types, Python sees an ambiguous expression, and does not guess which you want - it just

gives an error!

This is a traceback error. These occur when the code is being executed. In the last two lines it shows the line where the

error was found, and then a reason for the error. Not all reasons are immediately intelligible to a starting programmer,

but they are certainly worth checking out. In this case it is pretty direct. You need to make an explicit conversion, so

both are strings if you mean concatenation, ’7’ + str(2), or so both are int if you mean addition, int(’7’) +

With literal strings these examples are only useful for illustration: There is no reason to write such verbose expressions

when you already know the intended result. With variables, starting in the next section, expressions involving these

conversions become more important....

Be careful if you are a Java or C# programmer! This is unlike those languages, where the 2 would be automatically converted to ‘2’ so the

concatenation would make sense.

16 Chapter 1. Beginning With Python

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