Python masters and is familiar with list, ancestor, dictionary, and set data types

Sequence object (sequence)

"Sequence" is a data storage method often used in programming. In other programming languages, a "sequence" is often called an "array", a data structure used to store related data items. Almost every programming language provides "sequence" data structures, such as one-dimensional and multi-dimensional arrays in C and Basic.

The difference between a sequence and an array:

• An array provides a continuous memory space that can store the same data type.
• Although columns are continuous storage spaces, they can store different data types and can also be understood as more "advanced arrays".

[Sequence Object]

Commonly used sequence objects in python

• List List (variable data type).
• Tuple Tuple (immutable data type).
• Collection Sets (variable data type).
• Dictionary Dictionary (variable data type).
• String String (immutable).
• range( ).

1. List List (type)

• List (list) is the most frequently used data type in Python.
• Lists can complete the data structure implementation of most collection classes. It supports characters, numbers, strings and can even contain lists (i.e. nested).
• Lists are marked with "[ ]" and are the most common composite data type in python.

How to create a list

Syntax: List object name = [Element 1, Element 2, ..., Element N].

Example: Two ways to create a list object.

Method 1: Default method

列表对象= [元素1,元素2,元素3, ...元素N, ]
>>> list1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9,]
>>> list1
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list2 = [‘a’, ’b’, ‘c’, ‘d’, ‘e’, ‘f’, ]
>>> list2
[‘a’, ’b’, ‘c’, ‘d’, ‘e’, ‘f’]
>>> list3 = [‘a’, 1 , True , ‘Hello’, ]
>>> list3
[‘a’, 1 , True , ‘Hello’]

Example: Two ways to create a list object.

Method 2: Use range0 built-in function

• Python3 list) function is an object iterator, which can convert the iterable object returned by range() into a list, and the returned variable type for a list.

Syntax:

列表对象 = list(range(stop))
>>> list1 = list(range(10))
>>> list1
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list2 = list(range(5, 10))
>>> list2
[5, 6, 7, 8, 9]
>>> list3 = list(range(0, 10, 2))
>>> list3
[0, 2, 4, 6, 8]

Python3 range() built-in function

• Python3 range0 function returns an iterable object, not a list type, so When printing, the list will not be printed.

Creation syntax

① range( stop )
② range(start, stop [, step])

Parameter description:

• start: Counting starts from start. Default starts from 0. For example: range(5) is equivalent to range(0, 5).
• stop: Counts up to and including stop. For example: range(0, 5) is [0, 1, 2, 3, 4] without 5.
• step: step size, the default is 1. For example: range(0, 5) is equivalent to range(0, 5, 1).

How to access the list?

You can also use [head subscript: tail subscript: step] to cut the values ​​in the list, and you can intercept the corresponding list.

• The subscript index from left to right starts with 0 by default, and the subscript index from right to left starts with -1 by default. The subscript can be empty to indicate that the head or tail is retrieved.

Code demonstration: ch03-demol-it-slicepy

##Run result:

Can the first element in the mList be modified?

List update

The so-called update refers to the reassignment, deletion, and addition of list elements and other related operations.

Code demonstration: cho3-dem2-istupdate.py

##Running result:

List operators

We have already learned about the functions of and * in the introduction to strings. The usage of lists is similar to them, and there are also operations such as len() and in.

Code demonstration: ch03-demo03-list-operation.py

Run result:

Functions in lists

In order to better operate list objects, Python also provides a lot of functions:

① len(list) : 获取列表元素的个数;
② max(list) : 获取列表中的最大值;
③ min(list) : 获取列表中的最小值;
④ list(seq) : 将元组对象转换成列表对象。

Lists also provide a lot of methods:

① .append(obj) ：在列表末尾添加一个元素;
② .count(obj) : 统计某个元素在列表中出现的次数;
③ .index(obj) : 从列表中找出某个值第一个匹配的索引位置;
④ .insert(index, obj) : 向指定位置前序添加一个元素
⑤ .remove(obj) : 移除一个指定的元素;
⑥ .reverse() : 反向列表中的元素;
⑦ .sort() : 对列表进行排序;

The difference between List[] and list[:]

'[] "identification is a typical reference operation and address transfer operation.

• "[:]"identification, It is a typical assignment operation and value passing operation.
Sample code:

List_1 = [ 1, 2, 3, 4]
List_2 = list_1

List_1 = [ 1, 2, 3, 4]
List_2 = list_1[：]

2、元组(Tuple)类型

• Tuple(元组)类似于List(列表)。
• 元组不能二次赋值(元组内的元素不允许更新)，相当于只读列表。
• 元组用"() "标识。内部元素用逗号隔开。

如何创建元组?

语法：

元组对象名称 = ( 元素1， 元素 2， ……， 元素N )。

元组的特点

元组与列表的所有操作基本类似，唯一不一样的地方是，元组的元素不允许被修改。

示例代码：

>>> tup1 = tuple(range(5))
>>> tup1
(0, 1, 2, 3, 4)
>>> tup2 = (5, 6, 7,)
>>> tup2
(5, 6, 7)

特别说明：

>>> tup1 = s(1)
>>> type(tup1)
>>> tup1 =(1,)
>>> tup1

3、字典( Dictionary)类型

• 字典(dictionary)是除列表以外python之 中最灵活的内置数据结构类型。key:value
• 字典当中的元素是通过键来存取的 ,而不是通过偏移存取。
• 字典用"{}”标识。字典由索引(key)和它对应的值value组成，是一个典型的"k-v值”数据结构。

如何创建字典?

语法：

• 字典对象名称 = { }。
• 字典对象名称 = { key1 : value1, key2 : value2, …. , keyN : valueN}。

字典( Dictionary) k-v值在内存中的表现形式

Python 字典

• k-v结构- 般情况下在操作访问的时候都会使用key索弓进行每个元素的读取操作。
• 由于key索引键 会被频繁访问,因此索引键key存放在Stack栈内存中,而value值则存储在Heap堆内存中。

内存表现形式：

如何访问字典：

语法：

• 字典对象名称[ key ] #访问key对应的value值。
• 字典对象名称.keys #访问当前字典所有key索引键。
• 字典对象名称.values #访问当前字典所有valeus值。

代码演示: ch03-demo04.py

运行结果:

如何修改字典?

字典更新指的是对字段元素的重新赋值、删除、添加等相关操作。

相关方法：

• update( ) # 添加一个新元素或更新已有元素。
• pop( ) # 删除指定元素。

代码演示: cho3-demo05.py

运行结果 :

4、集合Set

• 集合是一个无序不重复元素的集。基本功能包括关系测试和消除重复元素。
• 可以用大括号({)创建集合。 注意:如果要创建一个空集合,你必须用set)而不是{} ;后者创建一个空的字典。

集合的创建

obj1 = {1, 2, 3, 4, 5}
obj2 = ({6, 7, 8, 9})

集合Set的关系操作(交.并、补)

s = set([3,5,9,10]) #创建- -个数值集合
t = set("Hello") #创建一个唯一 字符的集合
a=t|s # t和s的并集,
b=t&s # t和s的交集
C=t-S #求差集(项在t中,但不在s中)
d=t^s #对称差集(项在域s中,不会同时出现在二者中)

基本操作:

t.add('x") #添加一项
s.update([10,37,42]) #在s中添加多项

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