如何在Python中將子程序的結果同時輸出到文件和終端

當使用subprocess.call()時，可以指定檔案描述符作為outf 和errf 將stdout 和stderr 重定向到特定檔案。但是，這些結果不會同時顯示在終端機中。

使用Popen 和線程的解決方案：

為了克服這個問題，我們可以直接利用Popen 並利用stdout=PIPE 從子程序的stdout 讀取的參數。具體方法如下：

import subprocess
from threading import Thread

def tee(infile, *files):
    # Forward output from `infile` to `files` in a separate thread
    def fanout(infile, *files):
        for line in iter(infile.readline, ""):
            for f in files:
                f.write(line)

    t = Thread(target=fanout, args=(infile,)   files)
    t.daemon = True
    t.start()
    return t

def teed_call(cmd_args, **kwargs):
    # Override `stdout` and `stderr` arguments with PIPE to capture standard outputs
    stdout, stderr = [kwargs.pop(s, None) for s in ["stdout", "stderr"]]
    p = subprocess.Popen(
        cmd_args,
        stdout=subprocess.PIPE if stdout is not None else None,
        stderr=subprocess.PIPE if stderr is not None else None,
        **kwargs
    )
    
    # Create threads to simultaneously write to files and terminal
    threads = []
    if stdout is not None:
        threads.append(tee(p.stdout, stdout, sys.stdout))
    if stderr is not None:
        threads.append(tee(p.stderr, stderr, sys.stderr))
        
    # Join the threads to ensure IO completion before proceeding
    for t in threads:
        t.join()

    return p.wait()

使用此函數，我們可以執行子程序並將其輸出同時寫入檔案和終端：

outf, errf = open("out.txt", "wb"), open("err.txt", "wb")
teed_call(["cat", __file__], stdout=None, stderr=errf)
teed_call(["echo", "abc"], stdout=outf, stderr=errf, bufsize=0)
teed_call(["gcc", "a b"], close_fds=True, stdout=outf, stderr=errf)