Python不断阅读Popen（Windows） [英] Python reading Popen continuously (Windows)
问题描述
我尝试 stdout.readline 并在多处理过程中将结果（即每行打印到终端时）放入.Queue 我们在另一个.py文件中。但是，调用：
Im trying to stdout.readline and put the results (i.e each line, at the time of printing them to the terminal) on a multiprocessing.Queue for us in another .py file. However, the call:
res = subprocess.Popen(command, stdout=subprocess.PIPE, bufsize=1 )
with res.stdout:
for line in iter(res.stdout.readline, b''):
print line
res.wait()
在过程完成后将阻止并且将打印结果（如果退出代码不是，则根本不打印） t返回）。
Will block and the results will be printed after the process is complete (or not at all if exit code isn't returned).
我已经浏览了SO以获得答案，并尝试设置bufsize = 1，产生处理读数的线程，使用filedescriptor等。似乎无效。我可能不得不使用模块 pexpect 但我不确定它是如何工作的。
I've browsed SO for answers to this, and tried setting bufsize=1, spawning threads that handle the reading, using filedescriptors, etc. None seem to work. I might have to use the module pexpect but I'm not sure how it works yet.
我也试过
def enqueue_output(self, out, queue):
for line in iter(out.readline, b''):
queue.put([line])
out.close()
将数据放入队列，但由于 out.readline 似乎阻止了，结果将是相同的。
To put the data on the queue, but since out.readline seems to block, the result will be the same.
简而言之：如何在打印时将子进程输出提供给我？它一次打印1-10行的块，但是当这个过程完成时会返回给我，同时也用换行符分隔。
In short: How do I make the subprocess output available to me at the time of print? It prints chunks of 1-10 lines at a time, however these are returned to me when the process completes, separated by newlines as well..
相关：
Python ：从subprocess.communicate（）读取流媒体输入
在python上的subprocess.PIPE上的非阻塞读取
推荐答案
正如@eryksun所解释的那样，并且你的评论已经确认，缓冲的原因是C应用程序使用 printf 。
As explained by @eryksun, and confirmed by your comment, the cause of the buffering is the use of printf by the C application.
默认情况下，printf缓冲其输出，但输出在换行时刷新或者如果发生读取当输出定向到终端时。当输出定向到文件或管道时，实际输出仅在缓冲区已满时发生。
By default, printf buffers its output, but the output is flushed on newline or if a read occurs when the output is directed to a terminal. When the output is directed to a file or a pipe, the actual output only occurs when the buffer is full.
幸运的是，在Windows上，没有低级缓冲（* ）。这意味着在程序开头附近调用 setvbuf（stdout，NULL，_IONBF，0）; 就足够了。但不幸的是，你根本不需要缓冲（ _IONBF ），因为Windows上的行缓冲实现为完全缓冲。
Fortunately on Windows, there is no low level buffering (*). That means that calling setvbuf(stdout, NULL, _IONBF, 0); near the beginning of the program would be enough. But unfortunately, you need no buffering at all (_IONBF), because line buffering on Windows is implemented as full buffering.
（*）在Unix或Linux系统上，底层系统调用可以添加自己的缓冲。这意味着使用低级别 write（1，buf，strlen（buf））; 的程序将在Windows上无缓冲，但在标准输出时仍将在Linux上进行缓冲连接到管道或文件。
(*) On Unix or Linux systems, the underlying system call can add its own buffering. That means that a program using low level write(1, buf, strlen(buf)); will be unbuffered on Windows, but will still be buffered on Linux when standard output is connected to a pipe or a file.
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