在iter(fp.readline,'')而不是fp中的行: [英] line in iter(fp.readline, '') rather than line in fp:
问题描述
我在 iter 的示例rel =nofollow noreferrer>内置函数 - Python 3.7.0文档
I read builtin function iter
's example in Built-in Functions — Python 3.7.0 documentation
with open('mydata.txt') as fp:
for line in iter(fp.readline, ''):
process_line(line)
我无法弄清楚以下优势是什么:
I could not figure out what's the advantage over the following:
with open('mydata.txt') as fp:
for line in fp:
process_line(line)
你能否提供任何提示?
推荐答案
两者都会迭代生成器,而不会将整个文件加载到内存,但 iter()
版本正在演示使用 iter()的第二个参数
,定点
。
Both will iterate over a generator, without loading the whole file into memory, but the iter()
version is demonstrating the use of the second argument of iter()
, "sentinel
".
来自文档:
如果返回的值等于sentinel, StopIteration将被提升
if the value returned is equal to sentinel, StopIteration will be raised
所以此代码将从文件中读取,直到一行等于''
然后停止。
So this code will read from the file, until a line equals ''
and then stop.
这是一个奇怪的例子,因为文件中的所有行都会在末尾有换行符,所以这只会在文件末尾触发(如果在所有)。
This is a strange example, as all lines in the file will have a newline on the end, so this will only trigger at the end of the file anyway (if at all).
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