Python读取流 [英] Python read stream

问题描述

我需要一种非常的廉价方式来读取Python中没有终止字符串(流)的缓冲区.这就是我所拥有的，但是浪费了很多的CPU时间和精力.因为它是不断的尝试和捕捉".我真的需要一种新方法.

I need a very inexpensive way of reading a buffer with no terminating string (a stream) in Python. This is what I have, but it wastes a a lot of CPU time and effort. Because it is constantly "trying and catching." I really need a new approach.

这是我的代码的简化版本:

Here is a reduced working version of my code:

#! /usr/bin/env/ python
import fcntl, os, sys

if __name__ == "__main__":
    f = open("/dev/urandom", "r")
    fd = f.fileno()
    fl = fcntl.fcntl(fd, fcntl.F_GETFL)
    fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)

    ready = False
    line = ""
    while True:
        try:
            char = f.read()
            if char == '\r':
                continue
            elif char = '\n':
                ready = True
            else:
                line += char
        except:
            continue
        if ready:
            print line

请勿在终端中运行此命令.这只是为了说明. "urandom"将破坏您的终端，因为它吐出了很多随机字符，终端仿真器会解释这些字符，而不管它是什么(这可以更改您当前的shell设置，标题等).我正在阅读通过USB连接的GPS.

Don't run this in the terminal. It's simply for illustration. "urandom" will break your terminal because it spits out a lot of random characters that the terminal emulator interprets no matter what (which can change your current shells settings, title, etc). I was reading from a gps connected via usb.

问题:这可能会占用100％的CPU使用率.我已经尝试过了:

The problem: this uses 100% of the CPU usage when it can. I have tried this:

#! /usr/bin/env/ python
import fcntl, os, sys

if __name__ == "__main__":
    f = open("/dev/urandom", "r")
    fd = f.fileno()
    fl = fcntl.fcntl(fd, fcntl.F_GETFL)
    fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)

    for line in f.readlines():
        print line

但是，我得到了IOError: [Errno 11] Resource temporarily unavailable.除其他外，我尝试使用Popen.我很茫然.有人可以提供解决方案吗(请说明一切，因为我本身不是专业人士).另外，我应该注意，这是针对Unix(尤其是Linux，但必须可在所有版本的Linux上移植).

However, I get IOError: [Errno 11] Resource temporarily unavailable. I have tried to use Popen amongst other things. I am at a loss. Can someone please provide a solution (and please explain everything, as I am not a pro, per se). Also, I should note that this is for Unix (particularly Linux, but it must be portable across all versions of Linux).

推荐答案

打开文件流时，您需要将缓冲模式设置为要读取的块的大小. 来自python文档:

You will want to set your buffering mode to the size of the chunk you want to read when opening the file stream. From python documentation:

io.open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True)

" buffering 是用于设置缓冲策略的可选整数.传递0以关闭缓冲(仅在二进制模式下允许)，传递1以选择行缓冲(仅在文本模式下可用)，和大于1的整数表示固定大小的块缓冲区的大小."

"buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size of a fixed-size chunk buffer."

您还希望在while循环中使用visible()方法，以避免不必要的资源消耗.

You also want to use the readable() method in the while loop, to avoid unnecessary resource consumption.

但是，我建议您使用缓冲流，例如io.BytesIO或io.BufferedReader

However, I advise you to use buffered streams such as io.BytesIO or io.BufferedReader

文档中的更多信息.

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