Python next() 方法

Python next()函数返回迭代器的下一项。在本文中，我们将介绍next() 语法、next() 参数、next() 返回。

Syntax : next(iter, stopdef)

Parameters : 

• iter : The iterator over which iteration is to be performed.
• stopdef : Default value to be printed if we reach end of iterator.

Returns : Returns next element from the list, if not present prints the default value. If default value is not present, raises the StopIteration error.

Python next() 方法示例

示例 1：演示 next() 的工作原理

在这里，我们将在循环中看到Python next()。

Python3

# Python code to demonstrate
# working of next()
 
# initializing list
list1 = [1, 2, 3, 4, 5]
 
# converting list to iterator
list1 = iter(list1)
 
print("The contents of list are : ")
 
# printing using next()
# using default
while (1):
    val = next(list1, 'end')
    if val == 'end':
        print('list end')
        break
    else:
        print(val)

输出：

The contents of list are : 
1
2
3
4
5
list end

示例 2：从迭代器中获取下一项

Python3

list1 = [1, 2, 3, 4, 5]
 
# converting list to iterator
list1 = iter(list1)
 
print(list1)
print(next(list1))
print(next(list1))
print(next(list1))

输出：

1
2
3

示例 3：将默认值传递给 next()

Python3

list1 = [1, 2, 3, 4, 5]
 
# converting list to iterator
list1 = iter(list1)
 
print(list1)
print(next(list1, -1))
print(next(list1, -1))
print(next(list1, -1))
print(next(list1, -1))
print(next(list1, -1))
print(next(list1, -1))
print(next(list1, -1))

输出：

1
2
3
4
5
-1
-1

示例 6： Python next() 停止迭代

Python3

list1 = [1, 2, 3, 4, 5]
 
# converting list to iterator
list1 = iter(list1)
 
print(list1)
print(next(list1))
print(next(list1))
print(next(list1))
print(next(list1))
print(next(list1))
print(next(list1))

输出：

1
2
3
4
5
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
 in 
    10 print(next(list1))
    11 print(next(list1))
---> 12 print(next(list1))

StopIteration: 

当调用超出迭代器范围时，它会引发 Stopoteration 错误，为避免此错误，我们将使用默认值作为参数。

示例 5：性能分析

Python3

# Python code to demonstrate
# next() vs for loop
import time
 
# initializing list
list1 = [1, 2, 3, 4, 5]
 
# keeping list2
list2 = list1
 
# converting list to iterator
list1 = iter(list1)
 
print("The contents of list are : ")
 
# printing using next()
# using default
start_next = time.time()
while (1):
    val = next(list1, 'end')
    if val == 'end':
        break
    else:
        print(val)
print("Time taken for next() is : " + str(time.time() - start_next))
 
# printing using for loop
start_for = time.time()
for i in list2:
    print(i)
print("Time taken for loop is : " + str(time.time() - start_for))

输出：

The contents of list are : 
1
2
3
4
5
Time taken for next() is : 5.96046447754e-06
1
2
3
4
5
Time taken for loop is : 1.90734863281e-06

结果：在打印列表内容时，For 循环中的Python next是比 next() 更好的选择。

应用： next() 是打印 iter 类型容器组件的实用函数。它的用途是当容器的大小未知或者我们需要在列表/迭代器耗尽时给出提示。