Silence C++ stdout (stderr still works)

silence_pystan_output.py

import os
import sys
import threading
import pystan
import logging
# silence logger, there are better ways to do this
# see PyStan docs
logging.getLogger("pystan").propagate=False

def drain_pipe(captured_stdout, stdout_pipe):
    while True:
        data = os.read(stdout_pipe[0], 1024)
        if not data:
            break
        captured_stdout += data


def capture_output(function, *args, **kwargs):
    """
    https://stackoverflow.com/questions/24277488/in-python-how-to-capture-the-stdout-from-a-c-shared-library-to-a-variable
    """
    stdout_fileno = sys.stdout.fileno()
    stdout_save = os.dup(stdout_fileno)
    stdout_pipe = os.pipe()
    os.dup2(stdout_pipe[1], stdout_fileno)
    os.close(stdout_pipe[1])

    captured_stdout = b''

    t = threading.Thread(target=lambda:drain_pipe(captured_stdout, stdout_pipe))
    t.start()
    # run user function
    result = function(*args, **kwargs)
    os.close(stdout_fileno)
    t.join()
    os.close(stdout_pipe[0])
    os.dup2(stdout_save, stdout_fileno)
    os.close(stdout_save)
    return result, captured_stdout.decode("utf-8")
  
stan_code = """
parameters { 
    real y; 
}
model {
    y ~ normal(0,1);
}
"""

stan_model, _ = capture_output(pystan.StanModel, model_code=stan_code)
fit, _ = capture_output(stan_model.sampling)
print(fit)