What are the application methods of Python lists?

Python collection (array)

There are four collection data types in the Python programming language:

• List (List) is an ordered and changeable gather. Duplicate members are allowed.

• Tuple is an ordered and unchangeable collection. Duplicate members are allowed.

• Set is an unordered and unindexed collection. There are no duplicate members.

• A dictionary is an unordered, mutable and indexed collection. There are no duplicate members.

When choosing a collection type, it is useful to know the properties of that type.

Choosing the right type for a specific data set can mean preserving meaning, and it can mean improving efficiency or security.

List

A list is an ordered and changeable collection. In Python, lists are written using square brackets.

Instance

Create List:

thislist = ["apple", "banana", "cherry"]
print(thislist)

Run Instance

Access Project

You can access a list item by referencing the index number:

Example

Print the second item of the list:

thislist = ["apple", "banana", "cherry"]
print(thislist[1])

Run the example

Negative index

Negative index means starting from the end, -1 means the last item, -2 means the second to last item, and so on .

Example

Print the last item in the list:

thislist = ["apple", "banana", "cherry"]
print(thislist[-1])

Run the example

## Index range

You can specify an index range by specifying the start and end points of the range.

After specifying the range, the return value will be a new list containing the specified items.

Instance

Return the third, fourth, and fifth items:

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(thislist[2:5])

Run instance

Note: The search will start at index 2 (inclusive) and end at index 5 (exclusive).

Remember, the index of the first item is 0.

Range of negative index

If you want to search from the end of the list, please specify a negative index:

Example

This example Will return items from index -4 (included) to index -1 (excluded):

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(thislist[-4:-1])

Run instance

Change item value

To change the value of a specific item, quote the index number:

Instance

Change the second item:

thislist = ["apple", "banana", "cherry"]
thislist[1] = "mango"
print(thislist)

Run Example

Traverse the list

You can use a for loop to iterate over the list items:

Example

One by one Print all items in the list:

thislist = ["apple", "banana", "cherry"]
for x in thislist: 
    print(x)

Run Example

We will learn more about for loops in the chapter Python For Loops.

Check if an item exists

To determine whether a specified item exists in the list, use the in keyword:

Example

Check if "apple" exists in the list:

thislist = ["apple", "banana", "cherry"]
if "apple" in thislist:
  print("Yes, 'apple' is in the fruits list")

Running instance

List length

To determine how many are in the list items, please use the len() method:

Example

Print the number of items in the list:

thislist = ["apple", "banana", "cherry"]
print(len(thislist))

Run the example

Add item

To add an item to the end of the list, use the append() method:

Example

Use the append() method to append an item:

thislist = ["apple", "banana", "cherry"]
thislist.append("orange")
print(thislist)

Run the instance

To add an item at the specified index, use the insert() method :

Instance

Insert item as second position:

thislist = ["apple", "banana", "cherry"]
thislist.insert(1, "orange")
print(thislist)

Run instance

##Delete items

There are several ways to delete items from the list:

Example

The remove() method deletes the specified item:

thislist = ["apple", "banana", "cherry"]
thislist.remove("banana")
print(thislist)

Run the example

The pop() method deletes the specified index (if no index is specified, the last item is deleted):

thislist = ["apple", "banana", "cherry"]
thislist.pop()
print(thislist)

Run instance

实例

del 关键字删除指定的索引：

thislist = ["apple", "banana", "cherry"]
del thislist[0]
print(thislist)

运行实例

实例

del 关键字也能完整地删除列表：

thislist = ["apple", "banana", "cherry"]
del thislist

运行实例

实例

clear() 方法清空列表：

thislist = ["apple", "banana", "cherry"]
thislist.clear()
print(thislist)

运行实例

复制列表

您只能通过键入 list2 = list1 来复制列表，因为：list2 将只是对 list1 的引用，list1 中所做的更改也将自动在 list2 中进行。

有一些方法可以进行复制，一种方法是使用内置的 List 方法 copy()。

实例

使用 copy() 方法来复制列表：

thislist = ["apple", "banana", "cherry"]
mylist = thislist.copy()
print(mylist)

运行实例

制作副本的另一种方法是使用内建的方法 list()。

实例

使用 list() 方法复制列表：

thislist = ["apple", "banana", "cherry"]
mylist = list(thislist)
print(mylist)

运行实例

合并两个列表

在 Python 中，有几种方法可以连接或串联两个或多个列表。

最简单的方法之一是使用 + 运算符。

实例

合并两个列表：

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)

运行实例

连接两个列表的另一种方法是将 list2 中的所有项一个接一个地追加到 list1 中：

实例

把 list2 追加到 list1 中：

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
for x in list2: 
    list1.append(x)
    print(list1)

运行实例

或者，您可以使用 extend() 方法，其目的是将一个列表中的元素添加到另一列表中：

实例

使用 extend() 方法将 list2 添加到 list1 的末尾：

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
list1.extend(list2)
print(list1)

运行实例

list() 构造函数

也可以使用 list() 构造函数创建一个新列表。

实例

使用 list() 构造函数创建列表：

thislist = list(("apple", "banana", "cherry")) # 请注意双括号
print(thislist)

运行实例

列表方法

Python 有一组可以在列表上使用的内建方法。

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