您不能像这样使用p.stdout；如果您要求“整个标准输出”，则仅在过程终止（或填充管道缓冲区，这可能需要很长时间）时才可用。
您需要逐行从流程的标准输出中读取。
while True:
ln = p.stdout.readline()
if '' == ln:
break
m = re.search("Thread (?P<id>\d+)", ln);
if m:
# use m.group() to extract information
# e.g. m.group('id') will hold the 12345 from "Thread 12345"
最好将stdout设置为行缓冲（通常在可能的情况下完全缓冲），但是我认为这只能在被调用的程序中完成。
这里有两个要考虑的缓冲区。一种是C程序的输出缓冲区。这可能不存在（无缓冲输出），行缓冲或完全缓冲（1K，4K或8K是一些可能的大小）。
现在，输出进入Python的管道。再次可以完全缓冲（stdout）或行缓冲（readline）。因此输出为：
在后一种情况下，缓冲区将以4K块的形式进入Python逻辑。
现在让我们想象一下一个 C程序，它每秒将一条长1K字符的行输出到Python程序中（如果C程序已被完全缓冲，那么将无能为力！）
循环读取stdout，我们将看到（在for循环内）：
通过readline阅读将得到：
在这里，我运行“ ping -c 3 -i 2 127.0.0.1”，以便以两秒的间隔将三个数据包发送到本地主机。一次ping需要大约六秒钟。我从ping读取了输出，并打印了一个时间戳。ping的整个输出足够小，可以放入Python的完整缓冲区中。
#!/usr/bin/python
import subprocess
from time import gmtime, strftime
p = subprocess.Popen(["ping", "-c", "3", "-i", "2", "127.0.0.1"],
stdout=subprocess.PIPE)
for ln in p.stdout:
print strftime("%H:%M:%s", gmtime()) + " received " + ln
# Now I start the same process again, reading the input the other way.
p = subprocess.Popen(["ping", "-c", "3", "-i", "2", "127.0.0.1"],
stdout=subprocess.PIPE)
while True:
ln = p.stdout.readline()
if '' == ln:
break
print strftime("%H:%M:%s", gmtime()) + " received " + ln
我在Linux机器上收到的输出是预期的：
(nothing for the first six seconds)
15:40:10 received PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
15:40:10 received 64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.037 ms
15:40:10 received 64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.034 ms
15:40:10 received 64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.031 ms
15:40:10 received
15:40:10 received --- 127.0.0.1 ping statistics ---
15:40:10 received 3 packets transmitted, 3 received, 0% packet loss, time 3998ms
15:40:10 received rtt min/avg/max/mdev = 0.031/0.034/0.037/0.002 ms
15:40:10 received PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
15:40:10 received 64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.041 ms
15:40:12 received 64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.039 ms
15:40:14 received 64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.035 ms
15:40:14 received
15:40:14 received --- 127.0.0.1 ping statistics ---
15:40:14 received 3 packets transmitted, 3 received, 0% packet loss, time 3999ms
15:40:14 received rtt min/avg/max/mdev = 0.035/0.038/0.041/0.005 ms
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