List Python

Python 集合（数组）

Python 编程语言中有四种集合数据类型：

  • 列表（List）是一种有序和可更改的集合。允许重复的成员。
  • 元组（Tuple）是一种有序且不可更改的集合。允许重复的成员。
  • 集合（Set）是一个无序和无索引的集合。没有重复的成员。
  • 词典（Dictionary）是一个无序，可变和有索引的集合。没有重复的成员。

选择集合类型时，了解该类型的属性很有用。

为特定数据集选择正确的类型可能意味着保留含义，并且可能意味着提高效率或安全性。

列表

列表是一个有序且可更改的集合。在 Python 中，列表用方括号编写。

Instance

创建列表：

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

运行实例

访问项目

您可以通过引用索引号来访问列表项：

Instance

打印列表的第二项：

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

运行实例

负的索引

负索引表示从末尾开始，-1 表示最后一个项目，-2 表示倒数第二个项目，依此类推。

Instance

打印列表的最后一项：

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

运行实例

索引范围

您可以通过指定范围的起点和终点来指定索引范围。

指定范围后，返回值将是包含指定项目的新列表。

Instance

返回第三、第四、第五项：

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

运行实例

注释：搜索将从索引 2（包括）开始，到索引 5（不包括）结束。

请记住，第一项的索引为 0。

负索引的范围

如果要从列表末尾开始搜索，请指定负索引：

Instance

此例将返回从索引 -4（包括）到索引 -1（排除）的项目：

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

运行实例

更改项目值

如需更改特定项目的值，请引用索引号：

Instance

更改第二项：

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

运行实例

遍历列表

您可以使用 for 循环遍历列表项：

Instance

逐个打印列表中的所有项目：

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

运行实例

您将在 For Loop Python 这一章中学习有关 for 循环的更多知识。

检查项目是否存在

如需确定列表中是否存在指定的项，请使用 in 关键字：

Instance

检查列表中是否存在 “apple”：

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

运行实例

列表长度

如需确定列表中有多少项，请使用 len() 方法：

Instance

打印列表中的项目数：

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

运行实例

添加项目

如需将项目添加到列表的末尾，请使用 Ci gina Ci gina 方法：

Instance

Use Ci gina Ci gina 方法追加项目：

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

运行实例

要在指定的索引处添加项目，请使用 extend() 方法：

Instance

Insert item as the second position:

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

运行实例

Delete item

There are several methods to delete items from a list:

Instance

remove() Method to delete a specified item:

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

运行实例

Instance

insert() Method to delete a specified index (if no index is specified, the last item is deleted):

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

运行实例

Instance

del The keyword can delete a specified index:

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

运行实例

Instance

del The keyword can also completely delete the list:

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

运行实例

Instance

Ci gina Ci gina Method to clear the list:

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

运行实例

copy the list

You can only copy the list by typing list2 = list1 to copy the list, because:list2 The copy will only be list1 reference,list1 Changes made will also be automatically reflected in list2 in.

There are some methods to copy, one of which is to use the built-in List method Ci gina Method.

Instance

Use Ci gina Method Method to copy the list:

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

运行实例

Another method to make a copy is to use the built-in method list().

Instance

Use list() Method to copy the list:

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

运行实例

Merge two lists

In Python, there are several methods to concatenate or join two or more lists.

One of the simplest methods is to use the + operator.

Instance

Merge two lists:

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

运行实例

Another way to connect two lists is to append all items from list2 one by one to list1:

Instance

Append list2 to list1:

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

运行实例

Alternatively, you can use the extend() method, which is to add elements from one list to another:

Instance

Use the extend() method to add list2 to the end of list1:

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

运行实例

list() constructor function

You can also use list() The constructor function creates a new list.

Instance

Use list() Constructor function creates a list:

thislist = list(("apple", "banana", "cherry")) # Please note the parentheses
print(thislist)

运行实例

列表方法

print(thislist)

Method Ci gina
Ci gina Ci gina Ci gina Ci gina
Ci gina Ci gina Ci gina Ci gina
Ci gina Method Python ana gina da yau a yin a gina a cikin Ci gina.
Method Tana
append() clear()
copy() count()
extend() index()
insert() pop()
remove() remove()
reverse() reverse()
sort() Ci gina Ci gina