Python官方教程：从入门到控制流与数据结构

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本资源是Python官方文档，版本为3.7.1，由Guido van Rossum和Python开发团队编写，发布日期为2018年12月4日，由Python Software Foundation提供。这份文档旨在为初学者和经验丰富的开发者提供全面的Python教程和参考资料，特别适合想要深入了解Python语言、掌握其核心概念和高级特性的读者。文档内容分为多个章节，从入门到进阶，逐步深入： 1. **WhettingYourAppetite**：章节旨在激发学习者的兴趣，可能包含Python的基础语法和一些简单示例，让读者感受Python语言的简洁性和易用性。 2. **UsingthePythonInterpreter**：这部分讲解如何启动Python解释器以及交互式环境的使用，包括基本命令行输入和环境变量设置等。 3. **AnInformalIntroductiontoPython**：作为正式教程的起点，这里介绍Python作为计算器的功能，教授基础算术运算和表达式的处理，引导读者进入编程的基本逻辑。 4. **MoreControlFlowTools**：这一节详细介绍了控制流语句，如if-else语句、for循环、range函数、break和continue语句，以及pass语句和函数定义，帮助读者理解如何控制程序的流程。 5. **DataStructures**：涵盖列表（Lists）、del语句、元组（Tuples）和序列（Sequences）、集合（Sets）、字典（Dictionaries）等数据结构的使用，以及相关的遍历技术、条件判断和比较操作。 6. **Modules**：讲解模块的使用，包括标准库模块、dir()函数以及Python包（Packages），强调模块化编程的重要性和Python的模块管理工具。 7. **InputandOutput**：涉及更复杂的输出格式化和用户输入的处理，这是程序与外界交互的关键部分。通过阅读这份官方文档，读者可以系统地学习Python语言的基础知识，掌握编程核心技巧，并熟悉Python在实际项目中的应用。无论是初次接触Python还是想提升现有技能，这个文档都是一个宝贵的参考资料。

Python Tutorial, Release 3.7.1

Division (/) always returns a ﬂoat. To do ﬂoor division and get an integer result (discarding any fractional

result) you can use the // operator; to calculate the remainder you can use %:

>>> 17 / 3 # classic division returns a float

5.666666666666667

>>>

>>> 17 // 3 # floor division discards the fractional part

>>> 17 % 3 # the % operator returns the remainder of the division

>>> 5 * 3 + 2 # result * divisor + remainder

With Python, it is possible to use the ** operator to calculate powers

>>> 5 ** 2 # 5 squared

>>> 2 ** 7 # 2 to the power of 7

128

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 * 9

>>> width * height

900

If a variable is not “deﬁned” (assigned a value), trying to use it will give you an error:

>>> 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:

>>> 4 * 3.75 - 1

14.0

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

Since ** has higher precedence than -, -3**2 will be interpreted as -(3**2) and thus result in -9. To avoid this and get

9, you can use (-3)**2.

10 Chapter 3. An Informal Introduction to Python

Python Tutorial, Release 3.7.1

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.

In addition to int and float, Python supports other types of numbers, such as Decimal and Fraction.

Python also has built-in support for complex numbers, and uses the j or J suﬃx to indicate the imaginary

part (e.g. 3+5j).

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 ("...") with the same result

. \ can be used to escape

quotes:

>>> 'spam eggs' # single quotes

'spam eggs'

>>> 'doesn\'t' # use \' to escape the single quote...

"doesn't"

>>> "doesn't" # ...or use double quotes instead

"doesn't"

>>> '"Yes," they said.'

'"Yes," they said.'

>>> "\"Yes,\" they said."

'"Yes," they said.'

>>> '"Isn\'t," they said.'

'"Isn\'t," they said.'

In the interactive interpreter, the output string is enclosed in quotes and special characters are escaped with

backslashes. While this might sometimes look diﬀerent from the input (the enclosing quotes could change),

the two strings are equivalent. The string is enclosed in double quotes if the string contains a single quote

and no double quotes, otherwise it is enclosed in single quotes. The print() function produces a more

readable output, by omitting the enclosing quotes and by printing escaped and special characters:

>>> '"Isn\'t," they said.'

'"Isn\'t," they said.'

>>> print('"Isn\'t," they said.')

"Isn't," they said.

>>> s = 'First line.\nSecond line.' # \n means newline

>>> s # without print(), \n is included in the output

'First line.\nSecond line.'

>>> print(s) # with print(), \n produces a new line

First line.

Second line.

If you don’t want characters prefaced by \ to be interpreted as special characters, you can use raw strings

by adding an r before the ﬁrst quote:

>>> print('C:\some\name') # here \n means newline!

C:\some

ame

(continues on next page)

Unlike other languages, special characters such as \n have the same meaning with both single ('...') and double ("...")

quotes. The only diﬀerence between the two is that within single quotes you don’t need to escape " (but you have to escape

\') and vice versa.

3.1. Using Python as a Calculator 11

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