Here is my best attempt at asynchronously reading stdin/stdout from a subprocess and printing it from Python:
import asyncio
import subprocess
from asyncio.subprocess import STDOUT, PIPE, DEVNULL
async def start_stream():
return await asyncio.create_subprocess_shell(
'watch ls /proc',
stdout=PIPE,
stderr=PIPE,
limit=1024
)
async def spawn():
ev_proc = await start_stream()
while True:
stdout, stderr = await ev_proc.communicate()
print(stdout, stderr)
if __name__ == '__main__':
loop = asyncio.get_event_loop()
loop.run_until_complete(spawn())
Why is the print function not outputting anything?
Your watch
process never terminates and communicate()
waits for the process to terminate, therefore stdout
never arrives in your script.
https://docs.python.org/3/library/asyncio-subprocess.html
coroutine communicate(input=None)
Interact with process: Send data to stdin. Read data from stdout and stderr, until end-of-file is reached. Wait for process to terminate.
Try the following code which was inspired by https://stackoverflow.com/a/24435988/2776376 . It uses pipe_data_received
and then len > 16
is simply to prevent printing empty lines.
SubprocessProtocol.pipe_data_received(fd, data)
Called when the child process writes data into its stdout or stderr pipe. fd is the integer file descriptor of the pipe. data is a non-empty bytes object containing the data.
import asyncio
class SubprocessProtocol(asyncio.SubprocessProtocol):
def pipe_data_received(self, fd, data):
if fd == 1:
text = data.decode()
if len(text.strip()) > 16:
print(text.strip())
def process_exited(self):
loop.stop()
loop = asyncio.get_event_loop()
ls = loop.run_until_complete(loop.subprocess_exec(
SubprocessProtocol, 'watch', 'ls', '/proc'))
loop.run_forever()
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.