Python教程：从基础到高级特性

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本篇Python教程是根据Python之父Guido van Rossum的原著编写的，提供了一个全面且权威的学习指南。教程面向初学者，从基础的Python解释器使用开始，逐步引导读者探索语言的核心概念和高级特性。 **第1章：激发兴趣** 这一章节旨在吸引读者对Python语言产生兴趣，通过实例展示其简洁易用的特点，让学习者感受到Python作为编程语言的魅力。 **第2章：使用Python解释器** 2.1 节介绍如何调用Python解释器，包括命令行交互和脚本运行，让新手熟悉Python的基本执行环境。这部分强调了实践的重要性，通过实践来理解语言的基础操作。 2.2 节深入解析Python解释器的工作原理和环境设置，帮助学员了解程序执行过程中的变量、数据类型等基础知识。 **第3章：Python的初步认识** 3.1 部分教授如何使用Python进行基础数学计算，展示了编程的实用性。3.2 节则通过编写简单的程序，如计算器和条件语句，引导学习者步入编程的门槛。 **第4章：控制流工具** 这一部分详细讲解了if-else语句、for和while循环，以及break、continue、pass等控制结构，强调编程逻辑的构建和控制。 **5章：数据结构** 5.1 介绍了列表的基础操作，包括del语句用于修改和删除元素。5.2-5.5 分别讨论了元组、序列、集合和字典，这些数据结构是编程中必不可少的组成部分。 5.6-5.8 部分探讨了更复杂的循环技巧、条件判断和序列比较，提升代码的效率和可读性。 **第6章：模块与标准库** 6.1 展示了如何导入和使用模块，以及标准库的初步介绍。6.2 包含了Python内置的标准模块及其功能。6.3 讲解dir()函数，帮助学习者查找和理解模块中的函数和属性。6.4 探讨Python包的组织和管理。 **第7章：输入与输出** 7.1 着重于更高级的输出格式化，让读者能够创建更具吸引力和易读性的用户界面。这部分涵盖了文件处理、输入验证和用户交互等内容。这是一份循序渐进的Python教学资料，适合任何希望系统学习或提高Python技能的人士。无论是初次接触编程的新手，还是有一定经验的开发者，都能从中受益匪浅。通过跟随教程，学习者将逐步掌握Python语言的关键特性和实用技巧，为后续的项目开发打下坚实的基础。

Python Tutorial, Release 3.2.3

5.0

>>> 8/5 # Fractions aren’t lost when dividing integers

1.6

Note: You might not see exactly the same result; ﬂoating point results can differ from one machine to another. We will

say more later about controlling the appearance of ﬂoating point output. See also Floating Point Arithmetic: Issues

and Limitations for a full discussion of some of the subtleties of ﬂoating point numbers and their representations.

To do integer division and get an integer result, discarding any fractional result, there is another operator, //:

>>> # Integer division returns the floor:

... 7//3

>>> 7//-3

-3

The equal sign (’=’) is used to assign a value to a variable. Afterwards, no result is displayed before the next

interactive prompt:

>>> width = 20

>>> height = 5

>>> width

height

900

A value can be assigned to several variables simultaneously:

>>> x = y = z = 0 # Zero x, y and z

>>> x

>>> y

>>> z

Variables must be “deﬁned” (assigned a value) before they can be used, or an error will occur:

>>> # try to access an undefined variable

... n

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

NameError: name ’n’ is not defined

There is full support for ﬂoating point; operators with mixed type operands convert the integer operand to ﬂoating

point:

>>> 3

3.75 / 1.5

7.5

>>> 7.0 / 2

3.5

Complex numbers are also supported; imaginary numbers are written with a sufﬁx of j or J. Complex numbers with

a nonzero real component are written as (real+imagj), or can be created with the complex(real, imag)

function.

>>> 1j

(-1+0j)

>>> 1j

complex(0, 1)

(-1+0j)

>>> 3+1j

(3+3j)

10 Chapter 3. An Informal Introduction to Python

Python Tutorial, Release 3.2.3

’"Yes," he said.’

>>> "\"Yes,\" he said."

’"Yes," he said.’

>>> ’"Isn\’t," she said.’

’"Isn\’t," she said.’

The interpreter prints the result of string operations in the same way as they are typed for input: inside quotes, and with

quotes and other funny characters escaped by backslashes, to show the precise value. The string is enclosed in double

quotes if the string contains a single quote and no double quotes, else it’s enclosed in single quotes. The print()

function produces a more readable output for such input strings.

String literals can span multiple lines in several ways. Continuation lines can be used, with a backslash as the last

character on the line indicating that the next line is a logical continuation of the line:

hello = "This is a rather long string containing\n\

several lines of text just as you would do in C.\n\

Note that whitespace at the beginning of the line is\

significant."

print(hello)

Note that newlines still need to be embedded in the string using \n – the newline following the trailing backslash is

discarded. This example would print the following:

This is a rather long string containing

several lines of text just as you would do in C.

Note that whitespace at the beginning of the line is significant.

Or, strings can be surrounded in a pair of matching triple-quotes: """ or ”’. End of lines do not need to be escaped

when using triple-quotes, but they will be included in the string. So the following uses one escape to avoid an unwanted

initial blank line.

print("""\

Usage: thingy [OPTIONS]

-h Display this usage message

-H hostname Hostname to connect to

""")

produces the following output:

Usage: thingy [OPTIONS]

-h Display this usage message

-H hostname Hostname to connect to

If we make the string literal a “raw” string, \n sequences are not converted to newlines, but the backslash at the end

of the line, and the newline character in the source, are both included in the string as data. Thus, the example:

hello = r"This is a rather long string containing\n\

several lines of text much as you would do in C."

print(hello)

would print:

This is a rather long string containing\n\

several lines of text much as you would do in C.

Strings can be concatenated (glued together) with the + operator, and repeated with

>>> word = ’Help’ + ’A’

>>> word

12 Chapter 3. An Informal Introduction to Python

Python Tutorial, Release 3.2.3

Degenerate slice indices are handled gracefully: an index that is too large is replaced by the string size, an upper bound

smaller than the lower bound returns an empty string.

>>> word[1:100]

’elpA’

>>> word[10:]

’’

>>> word[2:1]

’’

Indices may be negative numbers, to start counting from the right. For example:

>>> word[-1] # The last character

’A’

>>> word[-2] # The last-but-one character

’p’

>>> word[-2:] # The last two characters

’pA’

>>> word[:-2] # Everything except the last two characters

’Hel’

But note that -0 is really the same as 0, so it does not count from the right!

>>> word[-0] # (since -0 equals 0)

’H’

Out-of-range negative slice indices are truncated, but don’t try this for single-element (non-slice) indices:

>>> word[-100:]

’HelpA’

>>> word[-10] # error

Traceback (most recent call last):

File "<stdin>", line 1, in ?

IndexError: string index out of range

One way to remember how slices work is to think of the indices as pointing between characters, with the left edge of

the ﬁrst character numbered 0. Then the right edge of the last character of a string of n characters has index n, for

example:

+---+---+---+---+---+

| H | e | l | p | A |

+---+---+---+---+---+

0 1 2 3 4 5

-5 -4 -3 -2 -1

The ﬁrst row of numbers gives the position of the indices 0...5 in the string; the second row gives the corresponding

negative indices. The slice from i to j consists of all characters between the edges labeled i and j, respectively.

For non-negative indices, the length of a slice is the difference of the indices, if both are within bounds. For example,

the length of word[1:3] is 2.

The built-in function len() returns the length of a string:

>>> s = ’supercalifragilisticexpialidocious’

>>> len(s)

Python教程：从基础到高级特性

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