子进程 ¶

创建子进程 ¶

coroutine asyncio. create_subprocess_exec ( program , *args , stdin=None , stdout=None , stderr=None , loop=None , limit=None , **kwds ) ¶

Create a subprocess.

limit argument sets the buffer limit for StreamReader wrappers for Process.stdout and Process.stderr (if subprocess.PIPE 会被传递给 stdout and stderr arguments).

返回 Process 实例。

See the documentation of loop.subprocess_exec() for other parameters.

从 3.8 版起弃用，将在 3.10 版中移除： loop 参数。

coroutine asyncio. create_subprocess_shell ( cmd , stdin=None , stdout=None , stderr=None , loop=None , limit=None , **kwds ) ¶

Run the cmd shell command.

limit argument sets the buffer limit for StreamReader wrappers for Process.stdout and Process.stderr (if subprocess.PIPE 会被传递给 stdout and stderr arguments).

返回 Process 实例。

See the documentation of loop.subprocess_shell() for other parameters.

Important

It is the application’s responsibility to ensure that all whitespace and special characters are quoted appropriately to avoid shell injection vulnerabilities. The shlex.quote() function can be used to properly escape whitespace and special shell characters in strings that are going to be used to construct shell commands.

从 3.8 版起弃用，将在 3.10 版中移除： loop 参数。

常量 ¶

asyncio.subprocess. PIPE ¶

Can be passed to the stdin , stdout or stderr 参数。

若 PIPE 会被传递给 stdin 自变量， Process.stdin attribute will point to a StreamWriter 实例。

若 PIPE 会被传递给 stdout or stderr arguments, the Process.stdout and Process.stderr attributes will point to StreamReader 实例。

asyncio.subprocess. STDOUT ¶

Special value that can be used as the stderr argument and indicates that standard error should be redirected into standard output.

asyncio.subprocess. DEVNULL ¶

Special value that can be used as the stdin , stdout or stderr argument to process creation functions. It indicates that the special file os.devnull will be used for the corresponding subprocess stream.

与子进程交互 ¶

Both create_subprocess_exec() and create_subprocess_shell() functions return instances of the Process 类。 Process is a high-level wrapper that allows communicating with subprocesses and watching for their completion.

class asyncio.subprocess. Process ¶

An object that wraps OS processes created by the create_subprocess_exec() and create_subprocess_shell() 函数。

This class is designed to have a similar API to the subprocess.Popen class, but there are some notable differences:

• unlike Popen, Process instances do not have an equivalent to the poll() 方法；

• communicate() and wait() methods don’t have a timeout parameter: use the wait_for() 函数；

• Process.wait() method is asynchronous, whereas subprocess.Popen.wait() method is implemented as a blocking busy loop;

• universal_newlines parameter is not supported.

此类是 非线程安全 .

另请参阅 子进程和线程 章节。

coroutine wait ( ) ¶

Wait for the child process to terminate.

设置并返回 returncode 属性。

注意

This method can deadlock when using stdout=PIPE or stderr=PIPE and the child process generates so much output that it blocks waiting for the OS pipe buffer to accept more data. Use the communicate() method when using pipes to avoid this condition.

coroutine communicate ( input=None ) ¶

Interact with process:

1. send data to stdin (if input 不是 None );

2. read data from stdout and stderr , until EOF is reached;

3. wait for process to terminate.

可选 input argument is the data ( bytes object) that will be sent to the child process.

返回元组 (stdout_data, stderr_data) .

If either BrokenPipeError or ConnectionResetError exception is raised when writing input into stdin , the exception is ignored. This condition occurs when the process exits before all data are written into stdin .

If it is desired to send data to the process’ stdin , the process needs to be created with stdin=PIPE . Similarly, to get anything other than None in the result tuple, the process has to be created with stdout=PIPE and/or stderr=PIPE 自变量。

Note, that the data read is buffered in memory, so do not use this method if the data size is large or unlimited.

send_signal ( signal ) ¶

发送信号 signal to the child process.

注意

在 Windows， SIGTERM 是别名化的 terminate() . CTRL_C_EVENT and CTRL_BREAK_EVENT can be sent to processes started with a creationflags parameter which includes CREATE_NEW_PROCESS_GROUP .

terminate ( ) ¶

停止子级进程。

On POSIX systems this method sends signal.SIGTERM to the child process.

On Windows the Win32 API function TerminateProcess() is called to stop the child process.

kill ( ) ¶

杀除子级进程。

On POSIX systems this method sends SIGKILL to the child process.

On Windows this method is an alias for terminate() .

stdin ¶

Standard input stream ( StreamWriter ) 或 None if the process was created with stdin=None .

stdout ¶

Standard output stream ( StreamReader ) 或 None if the process was created with stdout=None .

stderr ¶

Standard error stream ( StreamReader ) 或 None if the process was created with stderr=None .

警告

使用 communicate() method rather than process.stdin.write() , await process.stdout.read() or await process.stderr.read . This avoids deadlocks due to streams pausing reading or writing and blocking the child process.

pid ¶

Process identification number (PID).

Note that for processes created by the create_subprocess_shell() function, this attribute is the PID of the spawned shell.

returncode ¶

Return code of the process when it exits.

A None value indicates that the process has not terminated yet.

负值 -N 指示子级被终止，通过信号 N (仅 POSIX)。

import asyncio
import sys
async def get_date():
    code = 'import datetime; print(datetime.datetime.now())'
    # Create the subprocess; redirect the standard output
    # into a pipe.
    proc = await asyncio.create_subprocess_exec(
        sys.executable, '-c', code,
        stdout=asyncio.subprocess.PIPE)
    # Read one line of output.
    data = await proc.stdout.readline()
    line = data.decode('ascii').rstrip()
    # Wait for the subprocess exit.
    await proc.wait()
    return line
date = asyncio.run(get_date())
print(f"Current date: {date}")