列表方法append()和extend()之间有什么区别?


当前回答

append(object)通过将对象添加到列表来更新列表。

x = [20]
# List passed to the append(object) method is treated as a single object.
x.append([21, 22, 23])
# Hence the resultant list length will be 2
print(x)
--> [20, [21, 22, 23]]

extend(list)本质上连接两个列表。

x = [20]
# The parameter passed to extend(list) method is treated as a list.
# Eventually it is two lists being concatenated.
x.extend([21, 22, 23])
# Here the resultant list's length is 4
print(x)
--> [20, 21, 22, 23]

其他回答

append将元素添加到列表中。extend将第一个列表与另一个列表/可迭代列表连接起来。

>>> xs = ['A', 'B']
>>> xs
['A', 'B']

>>> xs.append("D")
>>> xs
['A', 'B', 'D']

>>> xs.append(["E", "F"])
>>> xs
['A', 'B', 'D', ['E', 'F']]

>>> xs.insert(2, "C")
>>> xs
['A', 'B', 'C', 'D', ['E', 'F']]

>>> xs.extend(["G", "H"])
>>> xs
['A', 'B', 'C', 'D', ['E', 'F'], 'G', 'H']

以下两个片段在语义上是等价的:

for item in iterator:
    a_list.append(item)

and

a_list.extend(iterator)

后者可能更快,因为循环是在C中实现的。

append():它基本上在Python中用于添加一个元素。

示例1:

>> a = [1, 2, 3, 4]
>> a.append(5)
>> print(a)
>> a = [1, 2, 3, 4, 5]

示例2:

>> a = [1, 2, 3, 4]
>> a.append([5, 6])
>> print(a)
>> a = [1, 2, 3, 4, [5, 6]]

extend():其中extend(()用于合并两个列表或在一个列表中插入多个元素。

示例1:

>> a = [1, 2, 3, 4]
>> b = [5, 6, 7, 8]
>> a.extend(b)
>> print(a)
>> a = [1, 2, 3, 4, 5, 6, 7, 8]

示例2:

>> a = [1, 2, 3, 4]
>> a.extend([5, 6])
>> print(a)
>> a = [1, 2, 3, 4, 5, 6]

追加和扩展是python中的扩展机制之一。

追加:将元素添加到列表末尾。

my_list = [1,2,3,4]

要向列表中添加新元素,我们可以按以下方式使用append方法。

my_list.append(5)

将添加新元素的默认位置始终位于(长度+1)位置。

Insert:Insert方法用于克服append的限制。使用insert,我们可以明确定义新元素插入的确切位置。

insert(索引,对象)的方法描述符。它需要两个参数,第一个是要插入元素的索引,第二个是元素本身。

Example: my_list = [1,2,3,4]
my_list[4, 'a']
my_list
[1,2,3,4,'a']

扩展:当我们想将两个或多个列表合并到一个列表中时,这非常有用。如果不使用extend,如果我们想要连接两个列表,那么生成的对象将包含一个列表列表。

a = [1,2]
b = [3]
a.append(b)
print (a)
[1,2,[3]]

如果我们试图访问位置2的元素,我们会得到一个列表([3]),而不是元素。要连接两个列表,我们必须使用append。

a = [1,2]
b = [3]
a.extend(b)
print (a)
[1,2,3]

加入多个列表

a = [1]
b = [2]
c = [3]
a.extend(b+c)
print (a)
[1,2,3]

append(object)通过将对象添加到列表来更新列表。

x = [20]
# List passed to the append(object) method is treated as a single object.
x.append([21, 22, 23])
# Hence the resultant list length will be 2
print(x)
--> [20, [21, 22, 23]]

extend(list)本质上连接两个列表。

x = [20]
# The parameter passed to extend(list) method is treated as a list.
# Eventually it is two lists being concatenated.
x.extend([21, 22, 23])
# Here the resultant list's length is 4
print(x)
--> [20, 21, 22, 23]