subprocess.py

# subprocess - Subprocesses with accessible I/O streams
#
# For more information about this module, see PEP 324.
#
# Copyright (c) 2003-2005 by Peter Astrand <astrand@lysator.liu.se>
#
# Licensed to PSF under a Contributor Agreement.

r"""Subprocesses with accessible I/O streams

This module allows you to spawn processes, connect to their
input/output/error pipes, and obtain their return codes.

For a complete description of this module see the Python documentation.

Main API
========
run(...): Runs a command, waits for it to complete, then returns a
          CompletedProcess instance.
Popen(...): A class for flexibly executing a command in a new process

Constants
---------
DEVNULL: Special value that indicates that os.devnull should be used
PIPE:    Special value that indicates a pipe should be created
STDOUT:  Special value that indicates that stderr should go to stdout


Older API
=========
call(...): Runs a command, waits for it to complete, then returns
    the return code.
check_call(...): Same as call() but raises CalledProcessError()
    if return code is not 0
check_output(...): Same as check_call() but returns the contents of
    stdout instead of a return code
getoutput(...): Runs a command in the shell, waits for it to complete,
    then returns the output
getstatusoutput(...): Runs a command in the shell, waits for it to complete,
    then returns a (exitcode, output) tuple
"""

import builtins
import errno
import io
import locale
import os
import time
import signal
import sys
import threading
import warnings
import contextlib
from time import monotonic as _time
import types

try:
    import fcntl
except ImportError:
    fcntl = None


__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
           "getoutput", "check_output", "run", "CalledProcessError", "DEVNULL",
           "SubprocessError", "TimeoutExpired", "CompletedProcess"]
           # NOTE: We intentionally exclude list2cmdline as it is
           # considered an internal implementation detail.  issue10838.

# use presence of msvcrt to detect Windows-like platforms (see bpo-8110)
try:
    import msvcrt
except ModuleNotFoundError:
    _mswindows = False
else:
    _mswindows = True

# some platforms do not support subprocesses
_can_fork_exec = sys.platform not in {"emscripten", "wasi", "ios", "tvos", "watchos"}

if _mswindows:
    import _winapi
    from _winapi import (CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP,  # noqa: F401
                         STD_INPUT_HANDLE, STD_OUTPUT_HANDLE,
                         STD_ERROR_HANDLE, SW_HIDE,
                         STARTF_USESTDHANDLES, STARTF_USESHOWWINDOW,
                         STARTF_FORCEONFEEDBACK, STARTF_FORCEOFFFEEDBACK,
                         ABOVE_NORMAL_PRIORITY_CLASS, BELOW_NORMAL_PRIORITY_CLASS,
                         HIGH_PRIORITY_CLASS, IDLE_PRIORITY_CLASS,
                         NORMAL_PRIORITY_CLASS, REALTIME_PRIORITY_CLASS,
                         CREATE_NO_WINDOW, DETACHED_PROCESS,
                         CREATE_DEFAULT_ERROR_MODE, CREATE_BREAKAWAY_FROM_JOB)

    __all__.extend(["CREATE_NEW_CONSOLE", "CREATE_NEW_PROCESS_GROUP",
                    "STD_INPUT_HANDLE", "STD_OUTPUT_HANDLE",
                    "STD_ERROR_HANDLE", "SW_HIDE",
                    "STARTF_USESTDHANDLES", "STARTF_USESHOWWINDOW",
                    "STARTF_FORCEONFEEDBACK", "STARTF_FORCEOFFFEEDBACK",
                    "STARTUPINFO",
                    "ABOVE_NORMAL_PRIORITY_CLASS", "BELOW_NORMAL_PRIORITY_CLASS",
                    "HIGH_PRIORITY_CLASS", "IDLE_PRIORITY_CLASS",
                    "NORMAL_PRIORITY_CLASS", "REALTIME_PRIORITY_CLASS",
                    "CREATE_NO_WINDOW", "DETACHED_PROCESS",
                    "CREATE_DEFAULT_ERROR_MODE", "CREATE_BREAKAWAY_FROM_JOB"])
else:
    if _can_fork_exec:
        from _posixsubprocess import fork_exec as _fork_exec
        # used in methods that are called by __del__
        class _del_safe:
            waitpid = os.waitpid
            waitstatus_to_exitcode = os.waitstatus_to_exitcode
            WIFSTOPPED = os.WIFSTOPPED
            WSTOPSIG = os.WSTOPSIG
            WNOHANG = os.WNOHANG
            ECHILD = errno.ECHILD
    else:
        class _del_safe:
            waitpid = None
            waitstatus_to_exitcode = None
            WIFSTOPPED = None
            WSTOPSIG = None
            WNOHANG = None
            ECHILD = errno.ECHILD

    import select
    import selectors


# Exception classes used by this module.
class SubprocessError(Exception): pass


class CalledProcessError(SubprocessError):
    """Raised when run() is called with check=True and the process
    returns a non-zero exit status.

    Attributes:
      cmd, returncode, stdout, stderr, output
    """
    def __init__(self, returncode, cmd, output=None, stderr=None):
        self.returncode = returncode
        self.cmd = cmd
        self.output = output
        self.stderr = stderr

    def __str__(self):
        if self.returncode and self.returncode < 0:
            try:
                return "Command '%s' died with %r." % (
                        self.cmd, signal.Signals(-self.returncode))
            except ValueError:
                return "Command '%s' died with unknown signal %d." % (
                        self.cmd, -self.returncode)
        else:
            return "Command '%s' returned non-zero exit status %d." % (
                    self.cmd, self.returncode)

    @property
    def stdout(self):
        """Alias for output attribute, to match stderr"""
        return self.output

    @stdout.setter
    def stdout(self, value):
        # There's no obvious reason to set this, but allow it anyway so
        # .stdout is a transparent alias for .output
        self.output = value


class TimeoutExpired(SubprocessError):
    """This exception is raised when the timeout expires while waiting for a
    child process.

    Attributes:
        cmd, output, stdout, stderr, timeout
    """
    def __init__(self, cmd, timeout, output=None, stderr=None):
        self.cmd = cmd
        self.timeout = timeout
        self.output = output
        self.stderr = stderr

    def __str__(self):
        return ("Command '%s' timed out after %s seconds" %
                (self.cmd, self.timeout))

    @property
    def stdout(self):
        return self.output

    @stdout.setter
    def stdout(self, value):
        # There's no obvious reason to set this, but allow it anyway so
        # .stdout is a transparent alias for .output
        self.output = value


if _mswindows:
    class STARTUPINFO:
        def __init__(self, *, dwFlags=0, hStdInput=None, hStdOutput=None,
                     hStdError=None, wShowWindow=0, lpAttributeList=None):
            self.dwFlags = dwFlags
            self.hStdInput = hStdInput
            self.hStdOutput = hStdOutput
            self.hStdError = hStdError
            self.wShowWindow = wShowWindow
            self.lpAttributeList = lpAttributeList or {"handle_list": []}

        def copy(self):
            attr_list = self.lpAttributeList.copy()
            if 'handle_list' in attr_list:
                attr_list['handle_list'] = list(attr_list['handle_list'])

            return STARTUPINFO(dwFlags=self.dwFlags,
                               hStdInput=self.hStdInput,
                               hStdOutput=self.hStdOutput,
                               hStdError=self.hStdError,
                               wShowWindow=self.wShowWindow,
                               lpAttributeList=attr_list)


    class Handle(int):
        closed = False

        def Close(self, CloseHandle=_winapi.CloseHandle):
            if not self.closed:
                self.closed = True
                CloseHandle(self)

        def Detach(self):
            if not self.closed:
                self.closed = True
                return int(self)
            raise ValueError("already closed")

        def __repr__(self):
            return "%s(%d)" % (self.__class__.__name__, int(self))

        __del__ = Close
else:
    # When select or poll has indicated that the file is writable,
    # we can write up to _PIPE_BUF bytes without risk of blocking.
    # POSIX defines PIPE_BUF as >= 512.
    _PIPE_BUF = getattr(select, 'PIPE_BUF', 512)

    # poll/select have the advantage of not requiring any extra file
    # descriptor, contrarily to epoll/kqueue (also, they require a single
    # syscall).
    if hasattr(selectors, 'PollSelector'):
        _PopenSelector = selectors.PollSelector
    else:
        _PopenSelector = selectors.SelectSelector


if _mswindows:
    # On Windows we just need to close `Popen._handle` when we no longer need
    # it, so that the kernel can free it. `Popen._handle` gets closed
    # implicitly when the `Popen` instance is finalized (see `Handle.__del__`,
    # which is calling `CloseHandle` as requested in [1]), so there is nothing
    # for `_cleanup` to do.
    #
    # [1] https://docs.microsoft.com/en-us/windows/desktop/ProcThread/
    # creating-processes
    _active = None

    def _cleanup():
        pass
else:
    # This lists holds Popen instances for which the underlying process had not
    # exited at the time its __del__ method got called: those processes are
    # wait()ed for synchronously from _cleanup() when a new Popen object is
    # created, to avoid zombie processes.
    _active = []

    def _cleanup():
        if _active is None:
            return
        for inst in _active[:]:
            res = inst._internal_poll(_deadstate=sys.maxsize)
            if res is not None:
                try:
                    _active.remove(inst)
                except ValueError:
                    # This can happen if two threads create a new Popen instance.
                    # It's harmless that it was already removed, so ignore.
                    pass

PIPE = -1
STDOUT = -2
DEVNULL = -3


# XXX This function is only used by multiprocessing and the test suite,
# but it's here so that it can be imported when Python is compiled without
# threads.

def _optim_args_from_interpreter_flags():
    """Return a list of command-line arguments reproducing the current
    optimization settings in sys.flags."""
    args = []
    value = sys.flags.optimize
    if value > 0:
        args.append('-' + 'O' * value)
    return args


def _args_from_interpreter_flags():
    """Return a list of command-line arguments reproducing the current
    settings in sys.flags, sys.warnoptions and sys._xoptions."""
    flag_opt_map = {
        'debug': 'd',
        # 'inspect': 'i',
        # 'interactive': 'i',
        'dont_write_bytecode': 'B',
        'no_site': 'S',
        'verbose': 'v',
        'bytes_warning': 'b',
        'quiet': 'q',
        # -O is handled in _optim_args_from_interpreter_flags()
    }
    args = _optim_args_from_interpreter_flags()
    for flag, opt in flag_opt_map.items():
        v = getattr(sys.flags, flag)
        if v > 0:
            args.append('-' + opt * v)

    if sys.flags.isolated:
        args.append('-I')
    else:
        if sys.flags.ignore_environment:
            args.append('-E')
        if sys.flags.no_user_site:
            args.append('-s')
        if sys.flags.safe_path:
            args.append('-P')

    # -W options
    warnopts = sys.warnoptions[:]
    xoptions = getattr(sys, '_xoptions', {})
    bytes_warning = sys.flags.bytes_warning
    dev_mode = sys.flags.dev_mode

    if bytes_warning > 1:
        warnopts.remove("error::BytesWarning")
    elif bytes_warning:
        warnopts.remove("default::BytesWarning")
    if dev_mode:
        warnopts.remove('default')
    for opt in warnopts:
        args.append('-W' + opt)

    # -X options
    if dev_mode:
        args.extend(('-X', 'dev'))
    for opt in ('faulthandler', 'tracemalloc', 'importtime',
                'frozen_modules', 'showrefcount', 'utf8', 'gil'):
        if opt in xoptions:
            value = xoptions[opt]
            if value is True:
                arg = opt
            else:
                arg = '%s=%s' % (opt, value)
            args.extend(('-X', arg))

    return args


def _text_encoding():
    # Return default text encoding and emit EncodingWarning if
    # sys.flags.warn_default_encoding is true.
    if sys.flags.warn_default_encoding:
        f = sys._getframe()
        filename = f.f_code.co_filename
        stacklevel = 2
        while f := f.f_back:
            if f.f_code.co_filename != filename:
                break
            stacklevel += 1
        warnings.warn("'encoding' argument not specified.",
                      EncodingWarning, stacklevel)

    if sys.flags.utf8_mode:
        return "utf-8"
    else:
        return locale.getencoding()


def call(*popenargs, timeout=None, **kwargs):
    """Run command with arguments.  Wait for command to complete or
    timeout, then return the returncode attribute.

    The arguments are the same as for the Popen constructor.  Example:

    retcode = call(["ls", "-l"])
    """
    with Popen(*popenargs, **kwargs) as p:
        try:
            return p.wait(timeout=timeout)
        except:  # Including KeyboardInterrupt, wait handled that.
            p.kill()
            # We don't call p.wait() again as p.__exit__ does that for us.
            raise


def check_call(*popenargs, **kwargs):
    """Run command with arguments.  Wait for command to complete.  If
    the exit code was zero then return, otherwise raise
    CalledProcessError.  The CalledProcessError object will have the
    return code in the returncode attribute.

    The arguments are the same as for the call function.  Example:

    check_call(["ls", "-l"])
    """
    retcode = call(*popenargs, **kwargs)
    if retcode:
        cmd = kwargs.get("args")
        if cmd is None:
            cmd = popenargs[0]
        raise CalledProcessError(retcode, cmd)
    return 0


def check_output(*popenargs, timeout=None, **kwargs):
    r"""Run command with arguments and return its output.

    If the exit code was non-zero it raises a CalledProcessError.  The
    CalledProcessError object will have the return code in the returncode
    attribute and output in the output attribute.

    The arguments are the same as for the Popen constructor.  Example:

    >>> check_output(["ls", "-l", "/dev/null"])
    b'crw-rw-rw- 1 root root 1, 3 Oct 18  2007 /dev/null\n'

    The stdout argument is not allowed as it is used internally.
    To capture standard error in the result, use stderr=STDOUT.

    >>> check_output(["/bin/sh", "-c",
    ...               "ls -l non_existent_file ; exit 0"],
    ...              stderr=STDOUT)
    b'ls: non_existent_file: No such file or directory\n'

    There is an additional optional argument, "input", allowing you to
    pass a string to the subprocess's stdin.  If you use this argument
    you may not also use the Popen constructor's "stdin" argument, as
    it too will be used internally.  Example:

    >>> check_output(["sed", "-e", "s/foo/bar/"],
    ...              input=b"when in the course of fooman events\n")
    b'when in the course of barman events\n'

    By default, all communication is in bytes, and therefore any "input"
    should be bytes, and the return value will be bytes.  If in text mode,
    any "input" should be a string, and the return value will be a string
    decoded according to locale encoding, or by "encoding" if set. Text mode
    is triggered by setting any of text, encoding, errors or universal_newlines.
    """
    for kw in ('stdout', 'check'):
        if kw in kwargs:
            raise ValueError(f'{kw} argument not allowed, it will be overridden.')

    if 'input' in kwargs and kwargs['input'] is None:
        # Explicitly passing input=None was previously equivalent to passing an
        # empty string. That is maintained here for backwards compatibility.
        if kwargs.get('universal_newlines') or kwargs.get('text') or kwargs.get('encoding') \
                or kwargs.get('errors'):
            empty = ''
        else:
            empty = b''
        kwargs['input'] = empty

    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
               **kwargs).stdout


class CompletedProcess(object):
    """A process that has finished running.

    This is returned by run().

    Attributes:
      args: The list or str args passed to run().
      returncode: The exit code of the process, negative for signals.
      stdout: The standard output (None if not captured).
      stderr: The standard error (None if not captured).
    """
    def __init__(self, args, returncode, stdout=None, stderr=None):
        self.args = args
        self.returncode = returncode
        self.stdout = stdout
        self.stderr = stderr

    def __repr__(self):
        args = ['args={!r}'.format(self.args),
                'returncode={!r}'.format(self.returncode)]
        if self.stdout is not None:
            args.append('stdout={!r}'.format(self.stdout))
        if self.stderr is not None:
            args.append('stderr={!r}'.format(self.stderr))
        return "{}({})".format(type(self).__name__, ', '.join(args))

    __class_getitem__ = classmethod(types.GenericAlias)


    def check_returncode(self):
        """Raise CalledProcessError if the exit code is non-zero."""
        if self.returncode:
            raise CalledProcessError(self.returncode, self.args, self.stdout,
                                     self.stderr)


def run(*popenargs,
        input=None, capture_output=False, timeout=None, check=False, **kwargs):
    """Run command with arguments and return a CompletedProcess instance.

    The returned instance will have attributes args, returncode, stdout and
    stderr. By default, stdout and stderr are not captured, and those attributes
    will be None. Pass stdout=PIPE and/or stderr=PIPE in order to capture them,
    or pass capture_output=True to capture both.

    If check is True and the exit code was non-zero, it raises a
    CalledProcessError. The CalledProcessError object will have the return code
    in the returncode attribute, and output & stderr attributes if those streams
    were captured.

    If timeout is given, and the process takes too long, a TimeoutExpired
    exception will be raised.

    There is an optional argument "input", allowing you to
    pass bytes or a string to the subprocess's stdin.  If you use this argument
    you may not also use the Popen constructor's "stdin" argument, as
    it will be used internally.

    By default, all communication is in bytes, and therefore any "input" should
    be bytes, and the stdout and stderr will be bytes. If in text mode, any
    "input" should be a string, and stdout and stderr will be strings decoded
    according to locale encoding, or by "encoding" if set. Text mode is
    triggered by setting any of text, encoding, errors or universal_newlines.

    The other arguments are the same as for the Popen constructor.
    """
    if input is not None:
        if kwargs.get('stdin') is not None:
            raise ValueError('stdin and input arguments may not both be used.')
        kwargs['stdin'] = PIPE

    if capture_output:
        if kwargs.get('stdout') is not None or kwargs.get('stderr') is not None:
            raise ValueError('stdout and stderr arguments may not be used '
                             'with capture_output.')
        kwargs['stdout'] = PIPE
        kwargs['stderr'] = PIPE

    with Popen(*popenargs, **kwargs) as process:
        try:
            stdout, stderr = process.communicate(input, timeout=timeout)
        except TimeoutExpired as exc:
            process.kill()
            if _mswindows:
                # Windows accumulates the output in a single blocking
                # read() call run on child threads, with the timeout
                # being done in a join() on those threads.  communicate()
                # _after_ kill() is required to collect that and add it
                # to the exception.
                exc.stdout, exc.stderr = process.communicate()
            else:
                # POSIX _communicate already populated the output so
                # far into the TimeoutExpired exception.
                process.wait()
            raise
        except:  # Including KeyboardInterrupt, communicate handled that.
            process.kill()
            # We don't call process.wait() as .__exit__ does that for us.
            raise
        retcode = process.poll()
        if check and retcode:
            raise CalledProcessError(retcode, process.args,
                                     output=stdout, stderr=stderr)
    return CompletedProcess(process.args, retcode, stdout, stderr)


def list2cmdline(seq):
    """
    Translate a sequence of arguments into a command line
    string, using the same rules as the MS C runtime:

    1) Arguments are delimited by white space, which is either a
       space or a tab.

    2) A string surrounded by double quotation marks is
       interpreted as a single argument, regardless of white space
       contained within.  A quoted string can be embedded in an
       argument.

    3) A double quotation mark preceded by a backslash is
       interpreted as a literal double quotation mark.

    4) Backslashes are interpreted literally, unless they
       immediately precede a double quotation mark.

    5) If backslashes immediately precede a double quotation mark,
       every pair of backslashes is interpreted as a literal
       backslash.  If the number of backslashes is odd, the last
       backslash escapes the next double quotation mark as
       described in rule 3.
    """

    # See
    # http://msdn.microsoft.com/en-us/library/17w5ykft.aspx
    # or search http://msdn.microsoft.com for
    # "Parsing C++ Command-Line Arguments"
    result = []
    needquote = False
    for arg in map(os.fsdecode, seq):
        bs_buf = []

        # Add a space to separate this argument from the others
        if result:
            result.append(' ')

        needquote = (" " in arg) or ("\t" in arg) or not arg
        if needquote:
            result.append('"')

        for c in arg:
            if c == '\\':
                # Don't know if we need to double yet.
                bs_buf.append(c)
            elif c == '"':
                # Double backslashes.
                result.append('\\' * len(bs_buf)*2)
                bs_buf = []
                result.append('\\"')
            else:
                # Normal char
                if bs_buf:
                    result.extend(bs_buf)
                    bs_buf = []
                result.append(c)

        # Add remaining backslashes, if any.
        if bs_buf:
            result.extend(bs_buf)

        if needquote:
            result.extend(bs_buf)
            result.append('"')

    return ''.join(result)


# Various tools for executing commands and looking at their output and status.
#

def getstatusoutput(cmd, *, encoding=None, errors=None):
    """Return (exitcode, output) of executing cmd in a shell.

    Execute the string 'cmd' in a shell with 'check_output' and
    return a 2-tuple (status, output). The locale encoding is used
    to decode the output and process newlines.

    A trailing newline is stripped from the output.
    The exit status for the command can be interpreted
    according to the rules for the function 'wait'. Example:

    >>> import subprocess
    >>> subprocess.getstatusoutput('ls /bin/ls')
    (0, '/bin/ls')
    >>> subprocess.getstatusoutput('cat /bin/junk')
    (1, 'cat: /bin/junk: No such file or directory')
    >>> subprocess.getstatusoutput('/bin/junk')
    (127, 'sh: /bin/junk: not found')
    >>> subprocess.getstatusoutput('/bin/kill $$')
    (-15, '')
    """
    try:
        data = check_output(cmd, shell=True, text=True, stderr=STDOUT,
                            encoding=encoding, errors=errors)
        exitcode = 0
    except CalledProcessError as ex:
        data = ex.output
        exitcode = ex.returncode
    if data[-1:] == '\n':
        data = data[:-1]
    return exitcode, data

def getoutput(cmd, *, encoding=None, errors=None):
    """Return output (stdout or stderr) of executing cmd in a shell.

    Like getstatusoutput(), except the exit status is ignored and the return
    value is a string containing the command's output.  Example:

    >>> import subprocess
    >>> subprocess.getoutput('ls /bin/ls')
    '/bin/ls'
    """
    return getstatusoutput(cmd, encoding=encoding, errors=errors)[1]



def _use_posix_spawn():
    """Check if posix_spawn() can be used for subprocess.

    subprocess requires a posix_spawn() implementation that properly reports
    errors to the parent process, & sets errno on the following failures:

    * Process attribute actions failed.
    * File actions failed.
    * exec() failed.

    Prefer an implementation which can use vfork() in some cases for best
    performance.
    """
    if _mswindows or not hasattr(os, 'posix_spawn'):
        # os.posix_spawn() is not available
        return False

    if sys.platform in ('darwin', 'sunos5'):
        # posix_spawn() is a syscall on both macOS and Solaris,
        # and properly reports errors
        return True

    # Check libc name and runtime libc version
    try:
        ver = os.confstr('CS_GNU_LIBC_VERSION')
        # parse 'glibc 2.28' as ('glibc', (2, 28))
        parts = ver.split(maxsplit=1)
        if len(parts) != 2:
            # reject unknown format
            raise ValueError
        libc = parts[0]
        version = tuple(map(int, parts[1].split('.')))

        if sys.platform == 'linux' and libc == 'glibc' and version >= (2, 24):
            # glibc 2.24 has a new Linux posix_spawn implementation using vfork
            # which properly reports errors to the parent process.
            return True
        # Note: Don't use the implementation in earlier glibc because it doesn't
        # use vfork (even if glibc 2.26 added a pipe to properly report errors
        # to the parent process).
    except (AttributeError, ValueError, OSError):
        # os.confstr() or CS_GNU_LIBC_VERSION value not available
        pass

    # By default, assume that posix_spawn() does not properly report errors.
    return False


# These are primarily fail-safe knobs for negatives. A True value does not
# guarantee the given libc/syscall API will be used.
_USE_POSIX_SPAWN = _use_posix_spawn()
_USE_VFORK = True
_HAVE_POSIX_SPAWN_CLOSEFROM = hasattr(os, 'POSIX_SPAWN_CLOSEFROM')


class Popen:
    """ Execute a child program in a new process.

    For a complete description of the arguments see the Python documentation.

    Arguments:
      args: A string, or a sequence of program arguments.

      bufsize: supplied as the buffering argument to the open() function when
          creating the stdin/stdout/stderr pipe file objects

      executable: A replacement program to execute.

      stdin, stdout and stderr: These specify the executed programs' standard
          input, standard output and standard error file handles, respectively.

      preexec_fn: (POSIX only) An object to be called in the child process
          just before the child is executed.

      close_fds: Controls closing or inheriting of file descriptors.

      shell: If true, the command will be executed through the shell.

      cwd: Sets the current directory before the child is executed.

      env: Defines the environment variables for the new process.

      text: If true, decode stdin, stdout and stderr using the given encoding
          (if set) or the system default otherwise.

      universal_newlines: Alias of text, provided for backwards compatibility.

      startupinfo and creationflags (Windows only)

      restore_signals (POSIX only)

      start_new_session (POSIX only)

      process_group (POSIX only)

      group (POSIX only)

      extra_groups (POSIX only)

      user (POSIX only)

      umask (POSIX only)

      pass_fds (POSIX only)

      encoding and errors: Text mode encoding and error handling to use for
          file objects stdin, stdout and stderr.

    Attributes:
        stdin, stdout, stderr, pid, returncode
    """
    _child_created = False  # Set here since __del__ checks it

    def __init__(self, args, bufsize=-1, executable=None,
                 stdin=None, stdout=None, stderr=None,
                 preexec_fn=None, close_fds=True,
                 shell=False, cwd=None, env=None, universal_newlines=None,
                 startupinfo=None, creationflags=0,
                 restore_signals=True, start_new_session=False,
                 pass_fds=(), *, user=None, group=None, extra_groups=None,
                 encoding=None, errors=None, text=None, umask=-1, pipesize=-1,
                 process_group=None):
        """Create new Popen instance."""
        if not _can_fork_exec:
            raise OSError(
                errno.ENOTSUP, f"{sys.platform} does not support processes."
            )

        _cleanup()
        # Held while anything is calling waitpid before returncode has been
        # updated to prevent clobbering returncode if wait() or poll() are
        # called from multiple threads at once.  After acquiring the lock,
        # code must re-check self.returncode to see if another thread just
        # finished a waitpid() call.
        self._waitpid_lock = threading.Lock()

        self._input = None
        self._communication_started = False
        if bufsize is None:
            bufsize = -1  # Restore default
        if not isinstance(bufsize, int):
            raise TypeError("bufsize must be an integer")

        if stdout is STDOUT:
            raise ValueError("STDOUT can only be used for stderr")

        if pipesize is None:
            pipesize = -1  # Restore default
        if not isinstance(pipesize, int):
            raise TypeError("pipesize must be an integer")

        if _mswindows:
            if preexec_fn is not None:
                raise ValueError("preexec_fn is not supported on Windows "
                                 "platforms")
        else:
            # POSIX
            if pass_fds and not close_fds:
                warnings.warn("pass_fds overriding close_fds.", RuntimeWarning)
                close_fds = True
            if startupinfo is not None:
                raise ValueError("startupinfo is only supported on Windows "
                                 "platforms")
            if creationflags != 0:
                raise ValueError("creationflags is only supported on Windows "
                                 "platforms")

        self.args = args
        self.stdin = None
        self.stdout = None
        self.stderr = None
        self.pid = None
        self.returncode = None
        self.encoding = encoding
        self.errors = errors
        self.pipesize = pipesize

        # Validate the combinations of text and universal_newlines
        if (text is not None and universal_newlines is not None
            and bool(universal_newlines) != bool(text)):
            raise SubprocessError('Cannot disambiguate when both text '
                                  'and universal_newlines are supplied but '
                                  'different. Pass one or the other.')

        self.text_mode = encoding or errors or text or universal_newlines
        if self.text_mode and encoding is None:
            self.encoding = encoding = _text_encoding()

        # How long to resume waiting on a child after the first ^C.
        # There is no right value for this.  The purpose is to be polite
        # yet remain good for interactive users trying to exit a tool.
        self._sigint_wait_secs = 0.25  # 1/xkcd221.getRandomNumber()

        self._closed_child_pipe_fds = False

        if self.text_mode:
            if bufsize == 1:
                line_buffering = True
                # Use the default buffer size for the underlying binary streams
                # since they don't support line buffering.
                bufsize = -1
            else:
                line_buffering = False

        if process_group is None:
            process_group = -1  # The internal APIs are int-only

        gid = None
        if group is not None:
            if not hasattr(os, 'setregid'):
                raise ValueError("The 'group' parameter is not supported on the "
                                 "current platform")

            elif isinstance(group, str):
                try:
                    import grp
                except ImportError:
                    raise ValueError("The group parameter cannot be a string "
                                     "on systems without the grp module")

                gid = grp.getgrnam(group).gr_gid
            elif isinstance(group, int):
                gid = group
            else:
                raise TypeError("Group must be a string or an integer, not {}"
                                .format(type(group)))

            if gid < 0:
                raise ValueError(f"Group ID cannot be negative, got {gid}")

        gids = None
        if extra_groups is not None:
            if not hasattr(os, 'setgroups'):
                raise ValueError("The 'extra_groups' parameter is not "
                                 "supported on the current platform")

            elif isinstance(extra_groups, str):
                raise ValueError("Groups must be a list, not a string")

            gids = []
            for extra_group in extra_groups:
                if isinstance(extra_group, str):
                    try:
                        import grp
                    except ImportError:
                        raise ValueError("Items in extra_groups cannot be "
                                         "strings on systems without the "
                                         "grp module")

                    gids.append(grp.getgrnam(extra_group).gr_gid)
                elif isinstance(extra_group, int):
                    gids.append(extra_group)
                else:
                    raise TypeError("Items in extra_groups must be a string "
                                    "or integer, not {}"
                                    .format(type(extra_group)))

            # make sure that the gids are all positive here so we can do less
            # checking in the C code
            for gid_check in gids:
                if gid_check < 0:
                    raise ValueError(f"Group ID cannot be negative, got {gid_check}")

        uid = None
        if user is not None:
            if not hasattr(os, 'setreuid'):
                raise ValueError("The 'user' parameter is not supported on "
                                 "the current platform")

            elif isinstance(user, str):
                try:
                    import pwd
                except ImportError:
                    raise ValueError("The user parameter cannot be a string "
                                     "on systems without the pwd module")
                uid = pwd.getpwnam(user).pw_uid
            elif isinstance(user, int):
                uid = user
            else:
                raise TypeError("User must be a string or an integer")

            if uid < 0:
                raise ValueError(f"User ID cannot be negative, got {uid}")

        # Input and output objects. The general principle is like
        # this:
        #
        # Parent                   Child
        # ------                   -----
        # p2cwrite   ---stdin--->  p2cread
        # c2pread    <--stdout---  c2pwrite
        # errread    <--stderr---  errwrite
        #
        # On POSIX, the child objects are file descriptors.  On
        # Windows, these are Windows file handles.  The parent objects
        # are file descriptors on both platforms.  The parent objects
        # are -1 when not using PIPEs. The child objects are -1
        # when not redirecting.

        (p2cread, p2cwrite,