How can the terminal output of executables run by Python functions be silenced in a general way?
Question:
I want to suppress all of the terminal output produced by a function that runs executables.
I have attempted to suppress the output of a Python function by using a context manager that temporarily redefines stdout and stderr each time the function is called. This suppresses terminal output produced by print calls in the function, but it doesn’t seem to work when the function calls executables that produce terminal output.
So, how could the output of executables called by Python functions be suppressed?
My code is below. I have included an example function that calls ls to try to illustrate the kind of terminal output I want to suppress (though the function I’m dealing with is different).
#!/usr/bin/env python
import os
import subprocess
import sys
def main():
print("hello")
with silence():
print("there")
print("world")
with silence():
engage_command(command = "ls")
class silence(object):
def __init__(
self,
stdout = None,
stderr = None
):
if stdout == None and stderr == None:
devnull = open(os.devnull, "w")
stdout = devnull
stderr = devnull
self._stdout = stdout or sys.stdout
self._stderr = stderr or sys.stderr
def __enter__(
self
):
self.old_stdout = sys.stdout
self.old_stderr = sys.stderr
self.old_stdout.flush()
self.old_stderr.flush()
sys.stdout = self._stdout
sys.stderr = self._stderr
def __exit__(
self,
exc_type,
exc_value,
traceback
):
self._stdout.flush()
self._stderr.flush()
sys.stdout = self.old_stdout
sys.stderr = self.old_stderr
def engage_command(
command = None
):
process = subprocess.Popen(
[command],
shell = True,
executable = "/bin/bash")
process.wait()
output, errors = process.communicate()
return output
if __name__ == "__main__":
main()
In my particular case, I’m trying to run the following function (instead of the ls function above):
with propyte.silence():
stream = pyaudio.PyAudio().open(
format = pyaudio.PyAudio().get_format_from_width(1),
channels = 1,
rate = bitrate,
output = True
)
When run, this produces output like the following:
ALSA lib pcm_dsnoop.c:606:(snd_pcm_dsnoop_open) unable to open slave
ALSA lib pcm_dmix.c:1029:(snd_pcm_dmix_open) unable to open slave
ALSA lib pcm.c:2266:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2266:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2266:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm_dmix.c:1029:(snd_pcm_dmix_open) unable to open slave
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for 4294967295, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for 4294967295, skipping unlock
I want to suppress that output.
EDIT: testing a solution provided by @Matthias
#!/usr/bin/env python
import contextlib
import os
import subprocess
import sys
def main():
print("hello")
with silence():
print("there")
print("world")
with silence():
engage_command(command = "ls")
@contextlib.contextmanager
def silence():
devnull = os.open(os.devnull, os.O_WRONLY)
old_stderr = os.dup(2)
sys.stderr.flush()
os.dup2(devnull, 2)
os.close(devnull)
try:
yield
finally:
os.dup2(old_stderr, 2)
os.close(old_stderr)
def engage_command(
command = None
):
process = subprocess.Popen(
[command],
shell = True,
executable = "/bin/bash")
process.wait()
output, errors = process.communicate()
return output
if __name__ == "__main__":
main()
I have not been successful in suppressing the terminal output from the print or the ls and I’m not sure why.
Answers:
For the ALSA errors in particular, you can use ALSA’s snd_lib_error_set_handler function as described for example in this question.
For one of my projects, I created a module called mute_alsa, which looks like this:
import ctypes
ERROR_HANDLER_FUNC = ctypes.CFUNCTYPE(None, ctypes.c_char_p, ctypes.c_int,
ctypes.c_char_p, ctypes.c_int,
ctypes.c_char_p)
def py_error_handler(filename, line, function, err, fmt):
pass
c_error_handler = ERROR_HANDLER_FUNC(py_error_handler)
try:
asound = ctypes.cdll.LoadLibrary('libasound.so.2')
asound.snd_lib_error_set_handler(c_error_handler)
except OSError:
pass
And you use it simply by putting the following into your code:
import mute_alsa
In a more general sense, you can prevent anything from printing to
stderr by simply closing the associated file descriptor. For
example, if we try to rm a file that doesn’t exist, we get an error
message printed to stderr:
>>> import sys
>>> import os
>>> os.system('rm /doesnotexist')
rm: cannot remove ‘/doesnotexist’: Is a directory
256
If we close the stderr file descriptor:
>>> os.close(sys.stderr.fileno())
We no longer see any error messages:
>>> os.system('rm /doesnotexist')
The downside to this approach is that it silences all messages to
stderr, which means you will no longer see legitimate error
messages. This may lead to surprising failure modes (the program
exited without printing any errors!).
You could switch from PyAudio to the sounddevice module, which already takes care of silencing the terminal output (see #12). This is how it is done there (using CFFI):
from cffi import FFI
import os
ffi = FFI()
ffi.cdef("""
/* from stdio.h */
FILE* fopen(const char* path, const char* mode);
int fclose(FILE* fp);
FILE* stderr; /* GNU C library */
FILE* __stderrp; /* Mac OS X */
""")
try:
stdio = ffi.dlopen(None)
devnull = stdio.fopen(os.devnull.encode(), b'w')
except OSError:
return
try:
stdio.stderr = devnull
except KeyError:
try:
stdio.__stderrp = devnull
except KeyError:
stdio.fclose(devnull)
If you want a pure Python solution, you can try this context manager:
import contextlib
import os
import sys
@contextlib.contextmanager
def ignore_stderr():
devnull = os.open(os.devnull, os.O_WRONLY)
old_stderr = os.dup(2)
sys.stderr.flush()
os.dup2(devnull, 2)
os.close(devnull)
try:
yield
finally:
os.dup2(old_stderr, 2)
os.close(old_stderr)
This is a very helpful blog post about the topic: http://eli.thegreenplace.net/2015/redirecting-all-kinds-of-stdout-in-python/.
UPDATE:
The context manager above silences the standard error output (stderr), which is used for the annoying messages from PortAudio mentioned in the original question. To get rid of the standard output (stdout), as in your updated question, you’ll have to replace sys.stderr with sys.stdout and the file descriptor 2 with the number 1:
@contextlib.contextmanager
def ignore_stdout():
devnull = os.open(os.devnull, os.O_WRONLY)
old_stdout = os.dup(1)
sys.stdout.flush()
os.dup2(devnull, 1)
os.close(devnull)
try:
yield
finally:
os.dup2(old_stdout, 1)
os.close(old_stdout)
Good afternoon, to resolve the errors, just add the following interpretation:
import sounddevice
If I need to install:
python3 -m pip install sounddevice
The easiest way to silence these executables without silencing your terminal is to import the sounddevice module.
pip -m install sounddevice
If you want to know more details about the sounddevice model read the documentation:
https://python-sounddevice.readthedocs.io/en/0.4.6/index.html
Summary of (sounddevice) Module:
It "provides bindings for the PortAudio library and a few convenience
functions to play and record NumPy arrays containing audio signals"
(python-sounddevice, version 0.4.6, 2019).
My Working Code:
import pyaudio
import wave
import sounddevice
FRAMES_PER_BUFFER = 3200
FORMAT = pyaudio.paInt16
CHANNELS = 1
RATE = 16000
p = pyaudio.PyAudio()
stream = p.open(
format=FORMAT,
channels=CHANNELS,
rate=RATE,
input=True,
frames_per_buffer=FRAMES_PER_BUFFER
)
print("start recording")
Output Before Import:
ALSA lib pcm.c:2664:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2664:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2664:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
@Rafhael P. Zrenner Thanks!!!! Because of your quick solution, I can continue working on my AI assistant using the pyttsx3 and SpeechRecognition modules.
I want to suppress all of the terminal output produced by a function that runs executables.
I have attempted to suppress the output of a Python function by using a context manager that temporarily redefines stdout and stderr each time the function is called. This suppresses terminal output produced by print calls in the function, but it doesn’t seem to work when the function calls executables that produce terminal output.
So, how could the output of executables called by Python functions be suppressed?
My code is below. I have included an example function that calls ls to try to illustrate the kind of terminal output I want to suppress (though the function I’m dealing with is different).
#!/usr/bin/env python
import os
import subprocess
import sys
def main():
print("hello")
with silence():
print("there")
print("world")
with silence():
engage_command(command = "ls")
class silence(object):
def __init__(
self,
stdout = None,
stderr = None
):
if stdout == None and stderr == None:
devnull = open(os.devnull, "w")
stdout = devnull
stderr = devnull
self._stdout = stdout or sys.stdout
self._stderr = stderr or sys.stderr
def __enter__(
self
):
self.old_stdout = sys.stdout
self.old_stderr = sys.stderr
self.old_stdout.flush()
self.old_stderr.flush()
sys.stdout = self._stdout
sys.stderr = self._stderr
def __exit__(
self,
exc_type,
exc_value,
traceback
):
self._stdout.flush()
self._stderr.flush()
sys.stdout = self.old_stdout
sys.stderr = self.old_stderr
def engage_command(
command = None
):
process = subprocess.Popen(
[command],
shell = True,
executable = "/bin/bash")
process.wait()
output, errors = process.communicate()
return output
if __name__ == "__main__":
main()
In my particular case, I’m trying to run the following function (instead of the ls function above):
with propyte.silence():
stream = pyaudio.PyAudio().open(
format = pyaudio.PyAudio().get_format_from_width(1),
channels = 1,
rate = bitrate,
output = True
)
When run, this produces output like the following:
ALSA lib pcm_dsnoop.c:606:(snd_pcm_dsnoop_open) unable to open slave
ALSA lib pcm_dmix.c:1029:(snd_pcm_dmix_open) unable to open slave
ALSA lib pcm.c:2266:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2266:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2266:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm_dmix.c:1029:(snd_pcm_dmix_open) unable to open slave
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for 4294967295, skipping unlock
JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for 4294967295, skipping unlock
I want to suppress that output.
EDIT: testing a solution provided by @Matthias
#!/usr/bin/env python
import contextlib
import os
import subprocess
import sys
def main():
print("hello")
with silence():
print("there")
print("world")
with silence():
engage_command(command = "ls")
@contextlib.contextmanager
def silence():
devnull = os.open(os.devnull, os.O_WRONLY)
old_stderr = os.dup(2)
sys.stderr.flush()
os.dup2(devnull, 2)
os.close(devnull)
try:
yield
finally:
os.dup2(old_stderr, 2)
os.close(old_stderr)
def engage_command(
command = None
):
process = subprocess.Popen(
[command],
shell = True,
executable = "/bin/bash")
process.wait()
output, errors = process.communicate()
return output
if __name__ == "__main__":
main()
I have not been successful in suppressing the terminal output from the print or the ls and I’m not sure why.
For the ALSA errors in particular, you can use ALSA’s snd_lib_error_set_handler function as described for example in this question.
For one of my projects, I created a module called mute_alsa, which looks like this:
import ctypes
ERROR_HANDLER_FUNC = ctypes.CFUNCTYPE(None, ctypes.c_char_p, ctypes.c_int,
ctypes.c_char_p, ctypes.c_int,
ctypes.c_char_p)
def py_error_handler(filename, line, function, err, fmt):
pass
c_error_handler = ERROR_HANDLER_FUNC(py_error_handler)
try:
asound = ctypes.cdll.LoadLibrary('libasound.so.2')
asound.snd_lib_error_set_handler(c_error_handler)
except OSError:
pass
And you use it simply by putting the following into your code:
import mute_alsa
In a more general sense, you can prevent anything from printing to
stderr by simply closing the associated file descriptor. For
example, if we try to rm a file that doesn’t exist, we get an error
message printed to stderr:
>>> import sys
>>> import os
>>> os.system('rm /doesnotexist')
rm: cannot remove ‘/doesnotexist’: Is a directory
256
If we close the stderr file descriptor:
>>> os.close(sys.stderr.fileno())
We no longer see any error messages:
>>> os.system('rm /doesnotexist')
The downside to this approach is that it silences all messages to
stderr, which means you will no longer see legitimate error
messages. This may lead to surprising failure modes (the program
exited without printing any errors!).
You could switch from PyAudio to the sounddevice module, which already takes care of silencing the terminal output (see #12). This is how it is done there (using CFFI):
from cffi import FFI
import os
ffi = FFI()
ffi.cdef("""
/* from stdio.h */
FILE* fopen(const char* path, const char* mode);
int fclose(FILE* fp);
FILE* stderr; /* GNU C library */
FILE* __stderrp; /* Mac OS X */
""")
try:
stdio = ffi.dlopen(None)
devnull = stdio.fopen(os.devnull.encode(), b'w')
except OSError:
return
try:
stdio.stderr = devnull
except KeyError:
try:
stdio.__stderrp = devnull
except KeyError:
stdio.fclose(devnull)
If you want a pure Python solution, you can try this context manager:
import contextlib
import os
import sys
@contextlib.contextmanager
def ignore_stderr():
devnull = os.open(os.devnull, os.O_WRONLY)
old_stderr = os.dup(2)
sys.stderr.flush()
os.dup2(devnull, 2)
os.close(devnull)
try:
yield
finally:
os.dup2(old_stderr, 2)
os.close(old_stderr)
This is a very helpful blog post about the topic: http://eli.thegreenplace.net/2015/redirecting-all-kinds-of-stdout-in-python/.
UPDATE:
The context manager above silences the standard error output (stderr), which is used for the annoying messages from PortAudio mentioned in the original question. To get rid of the standard output (stdout), as in your updated question, you’ll have to replace sys.stderr with sys.stdout and the file descriptor 2 with the number 1:
@contextlib.contextmanager
def ignore_stdout():
devnull = os.open(os.devnull, os.O_WRONLY)
old_stdout = os.dup(1)
sys.stdout.flush()
os.dup2(devnull, 1)
os.close(devnull)
try:
yield
finally:
os.dup2(old_stdout, 1)
os.close(old_stdout)
Good afternoon, to resolve the errors, just add the following interpretation:
import sounddevice
If I need to install:
python3 -m pip install sounddevice
The easiest way to silence these executables without silencing your terminal is to import the sounddevice module.
pip -m install sounddevice
If you want to know more details about the sounddevice model read the documentation:
https://python-sounddevice.readthedocs.io/en/0.4.6/index.html
Summary of (sounddevice) Module:
It "provides bindings for the PortAudio library and a few convenience
functions to play and record NumPy arrays containing audio signals"
(python-sounddevice, version 0.4.6, 2019).
My Working Code:
import pyaudio
import wave
import sounddevice
FRAMES_PER_BUFFER = 3200
FORMAT = pyaudio.paInt16
CHANNELS = 1
RATE = 16000
p = pyaudio.PyAudio()
stream = p.open(
format=FORMAT,
channels=CHANNELS,
rate=RATE,
input=True,
frames_per_buffer=FRAMES_PER_BUFFER
)
print("start recording")
Output Before Import:
ALSA lib pcm.c:2664:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2664:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2664:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
@Rafhael P. Zrenner Thanks!!!! Because of your quick solution, I can continue working on my AI assistant using the pyttsx3 and SpeechRecognition modules.