On Windows, the default event loop is SelectorEventLoop which does not support subprocesses. ProactorEventLoop should be used instead. Example to use it on Windows:
import asyncio, os
if os.name == 'nt':
loop = asyncio.ProactorEventLoop()
asyncio.set_event_loop(loop)
See also
Run the shell command cmd. See BaseEventLoop.subprocess_shell() for parameters. Return a Process instance.
The optional limit parameter sets the buffer limit passed to the StreamReader.
This function is a coroutine.
Create a subprocess. See BaseEventLoop.subprocess_exec() for parameters. Return a Process instance.
The optional limit parameter sets the buffer limit passed to the StreamReader.
This function is a coroutine.
Use the BaseEventLoop.connect_read_pipe() and BaseEventLoop.connect_write_pipe() methods to connect pipes.
Run subprocesses asynchronously using the subprocess module.
Create a subprocess from one or more string arguments (character strings or bytes strings encoded to the filesystem encoding), where the first string specifies the program to execute, and the remaining strings specify the program’s arguments. (Thus, together the string arguments form the sys.argv value of the program, assuming it is a Python script.) This is similar to the standard library subprocess.Popen class called with shell=False and the list of strings passed as the first argument; however, where Popen takes a single argument which is list of strings, subprocess_exec() takes multiple string arguments.
Other parameters:
Returns a pair of (transport, protocol), where transport is an instance of BaseSubprocessTransport.
This method is a coroutine.
See the constructor of the subprocess.Popen class for parameters.
Create a subprocess from cmd, which is a character string or a bytes string encoded to the filesystem encoding, using the platform’s “shell” syntax. This is similar to the standard library subprocess.Popen class called with shell=True.
See subprocess_exec() for more details about the remaining arguments.
Returns a pair of (transport, protocol), where transport is an instance of BaseSubprocessTransport.
This method is a coroutine.
See the constructor of the subprocess.Popen class for parameters.
See also
The BaseEventLoop.connect_read_pipe() and BaseEventLoop.connect_write_pipe() methods.
Special value that can be used as the stdin, stdout or stderr argument to create_subprocess_shell() and create_subprocess_exec() and indicates that a pipe to the standard stream should be opened.
Special value that can be used as the stderr argument to create_subprocess_shell() and create_subprocess_exec() and indicates that standard error should go into the same handle as standard output.
Special value that can be used as the stdin, stdout or stderr argument to create_subprocess_shell() and create_subprocess_exec() and indicates that the special file os.devnull will be used.
The identifier of the process.
Note that if you set the shell argument to True, this is the process identifier of the spawned shell.
Return code of the process when it exited. A None value indicates that the process has not terminated yet.
A negative value -N indicates that the child was terminated by signal N (Unix only).
Standard input stream (write), None if the process was created with stdin=None.
Standard output stream (read), None if the process was created with stdout=None.
Standard error stream (read), None if the process was created with stderr=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. The optional input argument should be data to be sent to the child process, or None, if no data should be sent to the child. The type of input must be bytes.
If a BrokenPipeError or ConnectionResetError exception is raised when writing input into stdin, the exception is ignored. It occurs when the process exits before all data are written into stdin.
communicate() returns a tuple (stdoutdata, stderrdata).
Note that if you want to send data to the process’s stdin, you need to create the Process object with stdin=PIPE. Similarly, to get anything other than None in the result tuple, you need to give stdout=PIPE and/or stderr=PIPE too.
Note
The data read is buffered in memory, so do not use this method if the data size is large or unlimited.
This method is a coroutine.
Changed in version 3.4.2: The method now ignores BrokenPipeError and ConnectionResetError.
Kills the child. On Posix OSs the function sends SIGKILL to the child. On Windows kill() is an alias for terminate().
Sends the signal signal to the child process.
Note
On Windows, SIGTERM is an alias for terminate(). CTRL_C_EVENT and CTRL_BREAK_EVENT can be sent to processes started with a creationflags parameter which includes CREATE_NEW_PROCESS_GROUP.
Stop the child. On Posix OSs the method sends signal.SIGTERM to the child. On Windows the Win32 API function TerminateProcess() is called to stop the child.
Wait for child process to terminate. Set and return returncode attribute.
This method is a coroutine.
Implement a function similar to subprocess.getstatusoutput(), except that it does not use a shell. Get the output of the “python -m platform” command and display the output:
import asyncio
import os
import sys
from asyncio import subprocess
@asyncio.coroutine
def getstatusoutput(*args):
proc = yield from asyncio.create_subprocess_exec(
*args,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
try:
stdout, _ = yield from proc.communicate()
except:
proc.kill()
yield from proc.wait()
raise
exitcode = yield from proc.wait()
return (exitcode, stdout)
if os.name == 'nt':
loop = asyncio.ProactorEventLoop()
asyncio.set_event_loop(loop)
else:
loop = asyncio.get_event_loop()
coro = getstatusoutput(sys.executable, '-m', 'platform')
exitcode, stdout = loop.run_until_complete(coro)
if not exitcode:
stdout = stdout.decode('ascii').rstrip()
print("Platform: %s" % stdout)
else:
print("Python failed with exit code %s:" % exitcode, flush=True)
sys.stdout.buffer.write(stdout)
sys.stdout.buffer.flush()
loop.close()