Python 简明教程

Python - Lists

Python Lists

列表是 Python 中内置的数据类型之一。Python 列表是由逗号分隔的项目序列，用方括号 [ ] 括起来。Python 列表中的项目不必是相同的数据类型。

List is one of the built-in data types in Python. A Python list is a sequence of comma separated items, enclosed in square brackets [ ]. The items in a Python list need not be of the same data type.

以下是一些 Python 列表示例：

Following are some examples of Python lists −

list1 = ["Rohan", "Physics", 21, 69.75]
list2 = [1, 2, 3, 4, 5]
list3 = ["a", "b", "c", "d"]
list4 = [25.50, True, -55, 1+2j]

列表是有序的项集合。列表中的每项都有一个从 0 开始的唯一位置索引。

List is an ordered collection of items. Each item in a list has a unique position index, starting from 0.

Python 中的列表类似于 C、C 或 Java 中的数组。但是，主要区别在于在 C/C/Java 中，数组元素必须是相同类型。另一方面，Python 列表可以包含不同数据类型的对象。

A list in Python is similar to an array in C, C or Java. However, the major difference is that in C/C/Java, the array elements must be of same type. On the other hand, Python lists may have objects of different data types.

Accessing Values in Lists

对于 access values in lists ，使用方括号，在进行切片时，可以根据索引或索引来获取在该索引位置可用的值。例如 −

To access values in lists, use the square brackets for slicing along with the index or indices to obtain value available at that index. For example −

list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5, 6, 7 ];
print ("list1[0]: ", list1[0])
print ("list2[1:5]: ", list2[1:5])

执行上述代码后，将生成以下结果 −

When the above code is executed, it produces the following result −

list1[0]:  physics
list2[1:5]:  [2, 3, 4, 5]

Updating Lists

您可以通过在赋值运算符的左侧给出切片来更新列表中的单个或多个元素，并且可以使用 append() 方法将元素添加到列表中。例如 −

You can update single or multiple elements of lists by giving the slice on the left-hand side of the assignment operator, and you can add to elements in a list with the append() method. For example −

list = ['physics', 'chemistry', 1997, 2000];
print ("Value available at index 2 : ")
print (list[2])
list[2] = 2001;
print ("New value available at index 2 : ")
print (list[2])

执行上述代码后，将生成以下结果 −

When the above code is executed, it produces the following result −

Value available at index 2 :
1997
New value available at index 2 :
2001

Delete List Elements

对于 remove a list element ，如果您确切知道要删除的元素，则可以使用 del 语句，如果您不知道，则可以使用 remove() 方法。例如 −

To remove a list element, you can use either the del statement if you know exactly which element(s) you are deleting or the remove() method if you do not know. For example −

list1 = ['physics', 'chemistry', 1997, 2000];
print (list1)
del list1[2];
print ("After deleting value at index 2 : ")
print (list1)

当执行以上代码时，它生成以下结果 −

When the above code is executed, it produces following result −

['physics', 'chemistry', 1997, 2000]
After deleting value at index 2 :
['physics', 'chemistry', 2000]

Note − remove() 方法将在后续章节中讨论。

Note − remove() method is discussed in subsequent section.

Python List Operations

在 Python 中，列表是一个序列。因此，我们可以使用“+”运算符连接两个列表，并使用“*”运算符连接列表的多个副本。成员运算符“in”和“not in”与列表对象一起使用。

In Python, List is a sequence. Hence, we can concatenate two lists with "+" operator and concatenate multiple copies of a list with "*" operator. The membership operators "in" and "not in" work with list object.

Indexing, Slicing, and Matrixes

由于列表是序列，因此索引和切片对列表的作用与对字符串的作用相同。

Because lists are sequences, indexing and slicing work the same way for lists as they do for strings.

假设以下输入 −

Assuming following input −

L = ['spam', 'Spam', 'SPAM!']

Python Expression

Results

Description

L[2]

SPAM!

Offsets start at zero

L[-2]

Spam

Negative: count from the right

L[1:]

['Spam', 'SPAM!']

Slicing fetches sections

Python List Methods

Python 包含以下列表方法 −

Python includes following list methods −

Sr.No.	Methods with Description
1	list.append(obj) Appends object obj to list.
2	list.clear() Clears the contents of list.
3	list.copy() Returns a copy of the list object.
4	list.count(obj) Returns count of how many times obj occurs in list
5	list.extend(seq) Appends the contents of seq to list
6	list.index(obj) Returns the lowest index in list that obj appears
7	list.insert(index, obj) Inserts object obj into list at offset index
8	list.pop(obj=list[-1]) Removes and returns last object or obj from list
9	list.remove(obj) Removes object obj from list
10	list.reverse() Reverses objects of list in place
11	list.sort([func]) Sorts objects of list, use compare func if given

Built-in Functions with Lists

以下是我们可以用于列表的内置函数 −

Following are the built-in functions we can use with lists −

Sr.No.	Function with Description
1	cmp(list1, list2)Compares elements of both lists.
2	len(list)Gives the total length of the list.
3	max(list)Returns item from the list with max value.
4	min(list)Returns item from the list with min value.
5	list(seq)Converts a tuple into list.