I'm using a python script as a driver for a hydrodynamics code. When it comes time to run the simulation, I use subprocess.Popen to run the code, collect the output from stdout and stderr into a subprocess.PIPE --- then I can print (and save to a log-file) the output information, and check for any errors. The problem is, I have no idea how the code is progressing. If I run it directly from the command line, it gives me output about what iteration its at, what time, what the next time-step is, etc.
是否有一种方法既存储输出(用于日志记录和错误检查)，又产生实时流输出?
我的代码的相关部分:
ret_val = subprocess.Popen( run_command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True )
output, errors = ret_val.communicate()
log_file.write(output)
print output
if( ret_val.returncode ):
print "RUN failed\n\n%s\n\n" % (errors)
success = False
if( errors ): log_file.write("\n\n%s\n\n" % errors)
最初，我将run_command通过tee输送，以便将副本直接发送到日志文件，流仍然直接输出到终端——但这样我就不能存储任何错误(据我所知)。
目前我的临时解决方案是:
ret_val = subprocess.Popen( run_command, stdout=log_file, stderr=subprocess.PIPE, shell=True )
while not ret_val.poll():
log_file.flush()
然后，在另一个终端上运行tail -f log.txt (s.t. log_file = 'log.txt')。
我找到了一个解决复杂问题的简单方法。
stdout和stderr都需要流化。
它们都需要是非阻塞的:当没有输出时，当有太多输出时。
不想使用Threading或multiprocessing，也不愿意使用pexpect。
这个解决方案使用了我在这里找到的一个要点
import subprocess as sbp
import fcntl
import os
def non_block_read(output):
fd = output.fileno()
fl = fcntl.fcntl(fd, fcntl.F_GETFL)
fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)
try:
return output.readline()
except:
return ""
with sbp.Popen('find / -name fdsfjdlsjf',
shell=True,
universal_newlines=True,
encoding='utf-8',
bufsize=1,
stdout=sbp.PIPE,
stderr=sbp.PIPE) as p:
while True:
out = non_block_read(p.stdout)
err = non_block_read(p.stderr)
if out:
print(out, end='')
if err:
print('E: ' + err, end='')
if p.poll() is not None:
break
Python 3的TLDR:
import subprocess
import sys
with open("test.log", "wb") as f:
process = subprocess.Popen(your_command, stdout=subprocess.PIPE)
for c in iter(lambda: process.stdout.read(1), b""):
sys.stdout.buffer.write(c)
f.buffer.write(c)
你有两种方法来做到这一点，要么从read或readline函数创建一个迭代器，然后做:
import subprocess
import sys
# replace "w" with "wb" for Python 3
with open("test.log", "w") as f:
process = subprocess.Popen(your_command, stdout=subprocess.PIPE)
# replace "" with b'' for Python 3
for c in iter(lambda: process.stdout.read(1), ""):
sys.stdout.write(c)
f.write(c)
or
import subprocess
import sys
# replace "w" with "wb" for Python 3
with open("test.log", "w") as f:
process = subprocess.Popen(your_command, stdout=subprocess.PIPE)
# replace "" with b"" for Python 3
for line in iter(process.stdout.readline, ""):
sys.stdout.write(line)
f.write(line)
或者您可以创建一个读取器和一个写入器文件。将写入器传递给Popen并从读取器读取
import io
import time
import subprocess
import sys
filename = "test.log"
with io.open(filename, "wb") as writer, io.open(filename, "rb", 1) as reader:
process = subprocess.Popen(command, stdout=writer)
while process.poll() is None:
sys.stdout.write(reader.read())
time.sleep(0.5)
# Read the remaining
sys.stdout.write(reader.read())
通过这种方式，您可以将数据写入test.log和标准输出中。
文件方法的唯一优点是代码不会阻塞。因此，您可以在此期间做任何您想做的事情，并以无阻塞的方式随时从阅读器读取。当您使用PIPE时，read和readline函数将阻塞，直到分别将一个字符写入管道或将一行字符写入管道。
在我看来，“来自subprocess命令的实时输出”意味着stdout和stderr都应该是实时的。stdin也应该被传递给子进程。
下面的片段在stdout和stderr上生成实时输出，并在outcome.{stdout,stderr}中将它们作为字节捕获。
窍门包括正确使用select和poll。
在Python 3.9上运行良好。
if self.log == 1:
print(f"** cmnd= {fullCmndStr}")
self.outcome.stdcmnd = fullCmndStr
try:
process = subprocess.Popen(
fullCmndStr,
shell=True,
encoding='utf8',
executable="/bin/bash",
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
)
except OSError:
self.outcome.error = OSError
else:
process.stdin.write(stdin)
process.stdin.close() # type: ignore
stdoutStrFile = io.StringIO("")
stderrStrFile = io.StringIO("")
pollStdout = select.poll()
pollStderr = select.poll()
pollStdout.register(process.stdout, select.POLLIN)
pollStderr.register(process.stderr, select.POLLIN)
stdoutEOF = False
stderrEOF = False
while True:
stdoutActivity = pollStdout.poll(0)
if stdoutActivity:
c= process.stdout.read(1)
if c:
stdoutStrFile.write(c)
if self.log == 1:
sys.stdout.write(c)
else:
stdoutEOF = True
stderrActivity = pollStderr.poll(0)
if stderrActivity:
c= process.stderr.read(1)
if c:
stderrStrFile.write(c)
if self.log == 1:
sys.stderr.write(c)
else:
stderrEOF = True
if stdoutEOF and stderrEOF:
break
if self.log == 1:
print(f"** cmnd={fullCmndStr}")
process.wait() # type: ignore
self.outcome.stdout = stdoutStrFile.getvalue()
self.outcome.stderr = stderrStrFile.getvalue()
self.outcome.error = process.returncode # type: ignore
我尝试过的所有上述解决方案都无法分离stderr和stdout输出(多个管道)，或者当操作系统管道缓冲区已满时永远阻塞，这发生在你运行输出太快的命令时(在python poll() subprocess手册上对此有警告)。我发现唯一可靠的方法是通过选择，但这是一个posix-only解决方案:
import subprocess
import sys
import os
import select
# returns command exit status, stdout text, stderr text
# rtoutput: show realtime output while running
def run_script(cmd,rtoutput=0):
p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
poller = select.poll()
poller.register(p.stdout, select.POLLIN)
poller.register(p.stderr, select.POLLIN)
coutput=''
cerror=''
fdhup={}
fdhup[p.stdout.fileno()]=0
fdhup[p.stderr.fileno()]=0
while sum(fdhup.values()) < len(fdhup):
try:
r = poller.poll(1)
except select.error, err:
if err.args[0] != EINTR:
raise
r=[]
for fd, flags in r:
if flags & (select.POLLIN | select.POLLPRI):
c = os.read(fd, 1024)
if rtoutput:
sys.stdout.write(c)
sys.stdout.flush()
if fd == p.stderr.fileno():
cerror+=c
else:
coutput+=c
else:
fdhup[fd]=1
return p.poll(), coutput.strip(), cerror.strip()
