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"""

Basic subprocess implementation for POSIX which only uses os functions. Only

implement features required by setup.py to build C extension modules when

subprocess is unavailable. setup.py is not used on Windows.

"""

import os

# distutils.spawn used by distutils.command.build_ext

# calls subprocess.Popen().wait()

class Popen:

def __init__(self, cmd, env=None):

self._cmd = cmd

self._env = env

self.returncode = None

def wait(self):

pid = os.fork()

if pid == 0:

# Child process

try:

if self._env is not None:

os.execve(self._cmd[0], self._cmd, self._env)

else:

os.execv(self._cmd[0], self._cmd)

finally:

os._exit(1)

else:

# Parent process

_, status = os.waitpid(pid, 0)

self.returncode = os.waitstatus_to_exitcode(status)

return self.returncode

def _check_cmd(cmd):

# Use regex [a-zA-Z0-9./-]+: reject empty string, space, etc.

safe_chars = []

for first, last in (("a", "z"), ("A", "Z"), ("0", "9")):

for ch in range(ord(first), ord(last) + 1):

safe_chars.append(chr(ch))

safe_chars.append("./-")

safe_chars = ''.join(safe_chars)

if isinstance(cmd, (tuple, list)):

check_strs = cmd

elif isinstance(cmd, str):

check_strs = [cmd]

else:

return False

for arg in check_strs:

if not isinstance(arg, str):

return False

if not arg:

# reject empty string

return False

for ch in arg:

if ch not in safe_chars:

return False

return True

# _aix_support used by distutil.util calls subprocess.check_output()

def check_output(cmd, **kwargs):

if kwargs:

raise NotImplementedError(repr(kwargs))

if not _check_cmd(cmd):

raise ValueError(f"unsupported command: {cmd!r}")

tmp_filename = "check_output.tmp"

if not isinstance(cmd, str):

cmd = " ".join(cmd)

cmd = f"{cmd} >{tmp_filename}"

try:

# system() spawns a shell

status = os.system(cmd)

exitcode = os.waitstatus_to_exitcode(status)

if exitcode:

raise ValueError(f"Command {cmd!r} returned non-zero "

f"exit status {exitcode!r}")

try:

with open(tmp_filename, "rb") as fp:

stdout = fp.read()

except FileNotFoundError:

stdout = b''

finally:

try:

os.unlink(tmp_filename)

except OSError:

pass

return stdout

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