读无限流-尾巴 [英] Reading infinite stream - tail

问题描述

问题:

程序从文件的末尾开始从无限流中读取行.

Problem:

Program to read the lines from infinite stream starting from its end of file.

#解决方案:

import time
def tail(theFile):
    theFile.seek(0,2)   # Go to the end of the file
    while True:
        line = theFile.readline()
        if not line:
            time.sleep(10)    # Sleep briefly for 10sec
            continue
        yield line

if __name__ == '__main__':
    fd = open('./file', 'r+')
    for line in tail(fd):
        print(line)

---

readline()是非阻塞读取，是否检查每一行.

---

readline() is a non-blocking read, with if check for every line.

问题:

在写入文件的进程具有close()

It does not make sense for my program running to wait infinitely, after the process writing to file has close()

1)为了避免if，此代码的EAFP方法是什么?

1) What would be the EAFP approach for this code, to avoid if?

2)生成器功能可以在file关闭时返回吗?

2) Can generator function return back on file close?

推荐答案

@ChristianDean在他的评论很好地回答了您的第一个问题，因此我将回答您的第二个问题.

@ChristianDean in his comment answered your first question quite nicely, so I'll answer your second.

我确实相信这是可能的-如果文件已关闭，则可以使用theFile的closed属性并引发StopIteration异常.像这样:

I do believe it is possible - you can use theFile's closed attribute and raise a StopIteration exception if the file was closed. Like this:

def tail(theFile):
    theFile.seek(0, 2) 
    while True:
        if theFile.closed:
            raise StopIteration

        line = theFile.readline()
        ...
        yield line

当文件关闭并且引发异常时，循环将停止.

Your loop shall cease when the file is closed and the exception is raised.

不涉及显式异常的更简洁的方法(感谢Christian Dean)是在循环头中测试文件指针.

A more succinct method (thanks, Christian Dean) that does not involve an explicit exception is to test the file pointer in the loop header.

def tail(theFile):
    theFile.seek(0, 2) 
    while not theFile.closed:
        line = theFile.readline()
        ...
        yield line

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