Python 3.6.4 官方教程详解

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"Python 3.6.4 官方教程是Python编程语言的一个详细学习指南，由Guido van Rossum及Python开发团队在2018年2月23日发布。本教程覆盖了Python的基础知识，包括使用Python解释器、控制流工具、数据结构、模块以及输入和输出等核心概念。" 在Python 3.6.4教程中，你可以了解到以下关键知识点： 1. **使用Python解释器**： - **启动解释器**: 你可以通过在命令行中输入`python3.6.4`来启动Python解释器。 - **交互模式**: 解释器提供了一个交互式环境，允许开发者即时测试代码片段和进行调试。 2. **Python作为计算器**： - Python支持基本的算术运算，如加、减、乘、除和取余，可以用于简单的数学计算。 3. **编程基础**： - **变量**: Python中的变量无需预先声明类型，可直接赋值使用。 - **字符串**: Python支持字符串操作，包括索引、切片和字符串格式化。 4. **控制流工具**： - **if语句**: 用于条件判断，根据条件执行不同的代码块。 - **for循环**: 常与range()函数配合使用，用于遍历序列或指定步长的范围。 - **while循环**: 当满足特定条件时，持续执行循环体。 - **break和continue**: break用于退出当前循环，continue则跳过当前迭代的剩余部分，继续下一轮循环。 - **pass语句**: 无实际操作的占位符，常用于定义空的代码块。 - **函数定义**: 使用`def`关键字定义函数，函数可以有参数和返回值。 5. **数据结构**： - **列表**: 动态大小的有序序列，支持索引和切片，可以包含不同类型的数据。 - **del语句**: 用于删除列表中的元素或整个列表。 - **元组**: 不可变序列，通常用作函数返回值或表示不可变数据集合。 - **集合**: 无序且不重复的元素集合，支持数学运算如并集、交集和差集。 - **字典**: 键值对的容器，通过键来访问对应的值，是Python中的动态关联数组。 6. **模块和包**： - **模块**: Python代码文件，可以包含变量、函数和类等，通过`import`语句引入。 - **标准库**: Python自带了许多预定义模块，如os、sys、math等，提供了丰富的功能。 - **dir()函数**: 显示模块或对象的属性和方法。 - **包**: 用于组织模块的命名空间，通过`.`分隔模块层次。 7. **输入和输出**： - **基本输出格式化**: 使用`print()`函数打印文本，支持字符串连接和格式化输出。 - **文件操作**: 文件的打开、读写、关闭，以及处理文本和二进制文件。 8. **其他**： - **异常处理**: Python使用`try/except`结构处理程序运行时的错误。 - **面向对象编程**: 包括类的定义、对象的创建、继承和多态等概念。 - **函数装饰器**: 用于修改或增强函数行为的特殊函数。这个教程不仅适合初学者入门，也对有经验的开发者有参考价值，因为它涵盖了Python的广泛特性。通过学习这些内容，你将能够熟练地编写、理解和维护Python程序。

Python Tutorial, Release 3.6.4

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

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.

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 3.6.4

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," he said.'

'"Yes," he said.'

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

'"Yes," he said.'

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

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

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

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

"Isn't," she 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

>>> print(r'C:\some\name') # note the r before the quote

C:\some\name

String literals can span multiple lines. One way is using triple-quotes: """...""" or '''...'''. End of

lines are automatically included in the string, but it’s possible to prevent this by adding a \ at the end of

the line. The following example:

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

Python Tutorial, Release 3.6.4

>>> word[-1] # last character

'n'

>>> word[-2] # second-last character

'o'

>>> word[-6]

'P'

Note that since -0 is the same as 0, negative indices start from -1.

In addition to indexing, slicing is also supported. While indexing is used to obtain individual characters,

slicing allows you to obtain substring:

>>> word[0:2] # characters from position 0 (included) to 2 (excluded)

'Py'

>>> word[2:5] # characters from position 2 (included) to 5 (excluded)

'tho'

Note how the start is always included, and the end always excluded. This makes sure that s[:i] + s[i:]

is always equal to s:

>>> word[:2] + word[2:]

'Python'

>>> word[:4] + word[4:]

'Python'

Slice indices have useful defaults; an omitted ﬁrst index defaults to zero, an omitted second index defaults

to the size of the string being sliced.

>>> word[:2] # character from the beginning to position 2 (excluded)

'Py'

>>> word[4:] # characters from position 4 (included) to the end

'on'

>>> word[-2:] # characters from the second-last (included) to the end

'on'

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:

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

| P | y | t | h | o | n |

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

0 1 2 3 4 5 6

-6 -5 -4 -3 -2 -1

The ﬁrst row of numbers gives the position of the indices 0…6 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.

Attempting to use an index that is too large will result in an error:

>>> word[42] # the word only has 6 characters

Traceback (most recent call last):

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

IndexError: string index out of range

3.1. Using Python as a Calculator 13

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