英文:
Subprocess Popen stdout is empty if the subprocess is a Python script
问题
以下是翻译好的部分：
这里有一些代码，应该在终端中打印出数字0到4：（修改自https://stackoverflow.com/a/59291466/4391249）
import os
import time
import subprocess
cmd = 'python', '-c', 'import time; [(print(i), time.sleep(1)) for i in range(5)]'
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
os.set_blocking(p.stdout.fileno(), False)
start = time.time()
while True:
# 在非阻塞模式下，第一次迭代始终产生空的字节字符串
line = p.stdout.readline()
if len(line):
print(line)
if time.time() > start + 5:
break
p.terminate()
但是对我来说并不起作用。对我来说，什么都没有被打印出来。
当我将cmd = 'ls'时，它会产生预期的输出（打印我的工作目录的内容）。
为什么Python版本不起作用？
我使用的是Ubuntu20.04和Python3.10。
英文:
Here is some code that should print numbers 0 through 4 to the terminal: (adapted from https://stackoverflow.com/a/59291466/4391249)
import os
import time
import subprocess
cmd = 'python', '-c', 'import time; [(print(i), time.sleep(1)) for i in range(5)]'
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
os.set_blocking(p.stdout.fileno(), False)
start = time.time()
while True:
# first iteration always produces empty byte string in non-blocking mode
line = p.stdout.readline()
if len(line):
print(line)
if time.time() > start + 5:
break
p.terminate()
But it doesn't for me. For me, nothing is printed.
When I instead set cmd = 'ls', it does produce the expected output (prints the contents of my working directory).
Why doesn't the Python one work?
I'm on Ubuntu20.04 with Python3.10.
答案1
得分: 1
禁用输出缓冲使用 -u 命令行标志：
import os
import time
import subprocess
cmd = [
'/Users/xyz/.pyenv/shims/python', '-u', '-c',
'import time; [(print(i), time.sleep(1)) for i in range(5)]';
]
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
os.set_blocking(p.stdout.fileno(), False)
start = time.time()
while True:
# 第一次迭代总是以非阻塞模式生成空的字节字符串
line = p.stdout.readline()
if len(line):
print(line)
if time.time() > start + 5:
break
p.terminate()
输出：
b'0\n'
b'1\n'
b'2\n'
b'3'
b'\n'
b'4\n'
英文:
Disable output buffering using -u cli flag:
import os
import time
import subprocess
cmd = [
'/Users/xyz/.pyenv/shims/python', '-u', '-c',
'import time; [(print(i), time.sleep(1)) for i in range(5)]'
]
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
os.set_blocking(p.stdout.fileno(), False)
start = time.time()
while True:
# first iteration always produces empty byte string in non-blocking mode
line = p.stdout.readline()
if len(line):
print(line)
if time.time() > start + 5:
break
p.terminate()
Out:
b'0\n'
b'1\n'
b'2\n'
b'3'
b'\n'
b'4\n'
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