如何使 PyAudio 的嘈杂输出静音？

Question

我已经安装了 PyAudio，它的工作方式完全符合我的要求，无论是播放还是录制音频。但是，每次我初始化一个PyAudio 对象时，它都会向 STDERR 发出一大堆警告和错误，这使得我很难对我自己的应用程序日志进行排序。这是一个 ipython 会话的示例：

In [1]: from pyaudio import PyAudio

In [2]: PyAudio()
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.hdmi.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4745:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5233:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM hdmi
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.hdmi.0:CARD=0,AES0=4,AES1=130,AES2=0,AES3=2'
ALSA lib conf.c:4745:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5233:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM hdmi
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4745:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5233:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline:CARD=0,DEV=0
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4745:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5233:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline:CARD=0,DEV=0
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4745:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5233:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM phoneline
ALSA lib confmisc.c:1281:(snd_func_refer) Unable to find definition 'cards.USB-Audio.pcm.modem.0:CARD=0'
ALSA lib conf.c:4745:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5233:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2660:(snd_pcm_open_noupdate) Unknown PCM phoneline
connect(2) call to /dev/shm/jack-1000/default/jack_0 failed (err=No such file or directory)
attempt to connect to server failed
connect(2) call to /dev/shm/jack-1000/default/jack_0 failed (err=No such file or directory)
attempt to connect to server failed
ALSA lib pcm_oss.c:377:(_snd_pcm_oss_open) Unknown field port
ALSA lib pcm_oss.c:377:(_snd_pcm_oss_open) Unknown field port
ALSA lib pcm_usb_stream.c:486:(_snd_pcm_usb_stream_open) Invalid type for card
ALSA lib pcm_usb_stream.c:486:(_snd_pcm_usb_stream_open) Invalid type for card
connect(2) call to /dev/shm/jack-1000/default/jack_0 failed (err=No such file or directory)
attempt to connect to server failed

Out[2]: <pyaudio.PyAudio at 0x7f7066350850>

我浏览了源代码，但找不到它在哪里喷出，据我所知，这不是通过 Python 的 logging 工具发生的，因为它会打印 []：

import logging
print([logging.getLogger(name) for name in logging.root.manager.loggerDict])

它似乎没有告诉我任何我需要知道的事情，所以我希望它只是......停下来。任何帮助将不胜感激。

Answer 1

问题是 PyAudio 在被调用时会加载一堆非 Python 的东西，而正是这些东西打印到 STDOUT，所以它必须直接静音。最简洁的方法是将其包装在上下文管理器中，以尽可能短的时间使STDOUT 静音：

import os

from pyaudio import PyAudio


class pyaudio:
    """
    PyAudio is noisy af every time you initialise it, which makes reading the
    log output rather difficult.  The output appears to be being made by the
    C internals, so I can't even redirect the logs with Python's logging
    facility.  Therefore the nuclear option was selected: swallow all stderr
    and stdout for the duration of PyAudio's use.

    Lifted and adapted from StackOverflow:
      https://stackoverflow.com/questions/11130156/
    """

    def __init__(self):

        # Open a pair of null files
        self.null_fds = [os.open(os.devnull, os.O_RDWR) for x in range(2)]

        # Save the actual stdout (1) and stderr (2) file descriptors.
        self.save_fds = [os.dup(1), os.dup(2)]

        self.pyaudio = None

    def __enter__(self) -> PyAudio:

        # Assign the null pointers to stdout and stderr.
        os.dup2(self.null_fds[0], 1)
        os.dup2(self.null_fds[1], 2)

        self.pyaudio = PyAudio()

        return self.pyaudio

    def __exit__(self, *_):

        self.pyaudio.terminate()

        # Re-assign the real stdout/stderr back to (1) and (2)
        os.dup2(self.save_fds[0], 1)
        os.dup2(self.save_fds[1], 2)

        # Close all file descriptors
        for fd in self.null_fds + self.save_fds:
            os.close(fd)

使用上面的样子是这样的：

with pyaudio() as audio:
    ...