python next()函数

最近在看python编程：从入门到实践里面读文件有用函数next()，对此函数不是很理解，看的代码如下：

import csv
filename='E:\python学习\pcc-master\chapter_16\sitka_weather_07-2014.csv'
with open(filename) as  f:
    reader=csv.reader(f)
    header_row=next(reader)
    for index,column_header in enumerate(header_row):
        print(index,column_header)

然后查了一下python的文档，里面的解释是The next() function returns the next item from the iterator.
这个函数的参数是迭代器（iterator）和一个default
next(iterator, default)
default是迭代器已经到了最末端，再调用next()函数的输出值。不填这个参数的话，到了最末端还用next()的话会报错。

random = [5, 9, 'cat']

# converting list to iterator
randomIterator = iter(random)
print(randomIterator)

# Output: 5
print(next(randomIterator))

# Output: 9
print(next(randomIterator))

# Output: 'cat'
print(next(randomIterator))

# This will raise Error
# iterator is exhausted
print(next(randomIterator))

这里的输出为

5
9
cat
Traceback (most recent call last):
File “python”, line 18, in
StopIteration
而添加了default之后的例子如下：

random = [5, 9]

# converting list to iterator
randomIterator = iter(random)

# Output: 5
print(next(randomIterator, '-1'))

# Output: 9
print(next(randomIterator, '-1'))

# randomIterator is exhausted
# Output: '-1'
print(next(randomIterator, '-1'))
print(next(randomIterator, '-1'))
print(next(randomIterator, '-1'))

输出如下：
5
9
-1
-1
-1

因此在python编程：从入门到实践里面的代码输入的是scv文件的迭代器，其指向文件的第一行，用了next之后，此迭代器指向文件的第二行，进行读取。