Python官方教程：从入门到数据结构与模块详解

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本资源是Python官方教程，由Guido van Rossum编写，适合英语水平良好的初学者阅读，特别是对于想要学习这门动态、简洁编程语言的人而言。教程在2012年10月发布，由Fred L. Drake Jr.担任编辑，由Python Software Foundation出版，文档地址为[docs@python.org](mailto:docs@python.org)。教程分为多个章节，旨在逐步引导读者熟悉Python语言。首先，第1章“WhettingYourAppetite”可能包含对Python语言的简单介绍，激发学习兴趣。第二章“Using the Python Interpreter”着重讲解如何使用Python解释器，包括如何调用解释器以及环境设置。在第3章“An Informal Introduction to Python”中，作者通过实例演示了Python的基本功能，如作为计算器的使用，以及如何进行基础编程操作。比如，学习者会学会如何使用if语句、for循环、range函数，以及如何理解break, continue和else在循环中的应用。此外，还介绍了pass语句和函数定义，同时强调了代码风格的重要性。进入第五章“Data Structures”，内容深入到列表（list）、del语句、元组（tuple）和序列（sequences）、集合（sets）、字典（dictionaries）等数据结构，以及如何利用这些结构实现复杂的逻辑控制。这一部分还包括了循环技巧、条件语句的进一步讲解以及不同类型的比较。第六章“Modules”探讨了模块的使用，包括标准模块、dir()函数的作用，以及Python包（packages）的概念，让学习者了解如何组织和复用代码。第七章“Input and Output”涉及更丰富的输出格式化，让学习者掌握如何处理用户输入和与外部系统的交互，确保程序能够有效地接收和输出信息。这份Python官方教程覆盖了从基本语法到数据结构、模块管理再到I/O操作的关键知识点，是学习Python编程的理想起点，适合希望通过实际例子和逐步指导快速上手的初学者。

Python Tutorial, Release 2.7.3

>>> 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:

>>> n # try to access an undefined variable

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)

>>> (3+1j)

(9+3j)

>>> (1+2j)/(1+1j)

(1.5+0.5j)

Complex numbers are always represented as two ﬂoating point numbers, the real and imaginary part. To extract

these parts from a complex number z, use z.real and z.imag.

>>> a=1.5+0.5j

>>> a.real

1.5

>>> a.imag

0.5

The conversion functions to ﬂoating point and integer (float(), int() and long()) don’t work for complex

numbers — there is no one correct way to convert a complex number to a real number. Use abs(z) to get its

magnitude (as a ﬂoat) or z.real to get its real part.

10 Chapter 3. An Informal Introduction to Python

Python Tutorial, Release 2.7.3

>>> a=3.0+4.0j

>>> float(a)

Traceback (most recent call last):

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

TypeError: can’t convert complex to float; use abs(z)

>>> a.real

3.0

>>> a.imag

4.0

>>> abs(a) # sqrt(a.real

2 + a.imag

5.0

In interactive mode, the last printed expression is assigned to the variable _. This means that when you are using

Python as a desk calculator, it is somewhat easier to continue calculations, for example:

>>> tax = 12.5 / 100

>>> price = 100.50

>>> price

tax

12.5625

>>> price + _

113.0625

>>> round(_, 2)

113.06

This variable should be treated as read-only by the user. Don’t explicitly assign a value to it — you would create

an independent local variable with the same name masking the built-in variable with its magic behavior.

3.1.2 Strings

Besides numbers, Python can also manipulate strings, which can be expressed in several ways. They can be

enclosed in single quotes or double quotes:

>>> ’spam eggs’

’spam eggs’

>>> ’doesn\’t’

"doesn’t"

>>> "doesn’t"

"doesn’t"

>>> ’"Yes," he said.’

’"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 statement 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

3.1. Using Python as a Calculator 11

Python Tutorial, Release 2.7.3

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.

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

’HelpA’

>>> ’<’ + word

5 + ’>’

’<HelpAHelpAHelpAHelpAHelpA>’

Two string literals next to each other are automatically concatenated; the ﬁrst line above could also have been

written word = ’Help’ ’A’; this only works with two literals, not with arbitrary string expressions:

>>> ’str’ ’ing’ # <- This is ok

’string’

>>> ’str’.strip() + ’ing’ # <- This is ok

’string’

>>> ’str’.strip() ’ing’ # <- This is invalid

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

’str’.strip() ’ing’

SyntaxError: invalid syntax

Strings can be subscripted (indexed); like in C, the ﬁrst character of a string has subscript (index) 0. There is no

separate character type; a character is simply a string of size one. Like in Icon, substrings can be speciﬁed with

the slice notation: two indices separated by a colon.

>>> word[4]

’A’

>>> word[0:2]

’He’

>>> word[2:4]

’lp’

12 Chapter 3. An Informal Introduction to Python

Python Tutorial, Release 2.7.3

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)

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