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Provides the 'spawn()' function, a front-end to various platform-
specific functions for launching another program in a sub-process.
Also provides the 'find_executable()' to search the path for a given
executable name.
import sys
import os
from distutils.errors import DistutilsPlatformError, DistutilsExecError
from distutils.debug import DEBUG
from distutils import log
def spawn(cmd, search_path=1, verbose=0, dry_run=0):
"""Run another program, specified as a command list 'cmd', in a new process.
'cmd' is just the argument list for the new process, ie.
cmd[0] is the program to run and cmd[1:] are the rest of its arguments.
There is no way to run a program with a name different from that of its
If 'search_path' is true (the default), the system's executable
search path will be used to find the program; otherwise, cmd[0]
must be the exact path to the executable. If 'dry_run' is true,
the command will not actually be run.
Raise DistutilsExecError if running the program fails in any way; just
return on success.
# cmd is documented as a list, but just in case some code passes a tuple
# in, protect our %-formatting code against horrible death
cmd = list(cmd)
if == 'posix':
_spawn_posix(cmd, search_path, dry_run=dry_run)
elif == 'nt':
_spawn_nt(cmd, search_path, dry_run=dry_run)
raise DistutilsPlatformError(
"don't know how to spawn programs on platform '%s'" %
def _nt_quote_args(args):
"""Quote command-line arguments for DOS/Windows conventions.
Just wraps every argument which contains blanks in double quotes, and
returns a new argument list.
# XXX this doesn't seem very robust to me -- but if the Windows guys
# say it'll work, I guess I'll have to accept it. (What if an arg
# contains quotes? What other magic characters, other than spaces,
# have to be escaped? Is there an escaping mechanism other than
# quoting?)
for i, arg in enumerate(args):
if ' ' in arg:
args[i] = '"%s"' % arg
return args
def _spawn_nt(cmd, search_path=1, verbose=0, dry_run=0):
executable = cmd[0]
cmd = _nt_quote_args(cmd)
if search_path:
# either we find one or it stays the same
executable = find_executable(executable) or executable' '.join([executable] + cmd[1:]))
if not dry_run:
# spawn for NT requires a full path to the .exe
rc = os.spawnv(os.P_WAIT, executable, cmd)
except OSError as exc:
# this seems to happen when the command isn't found
if not DEBUG:
cmd = executable
raise DistutilsExecError(
"command %r failed: %s" % (cmd, exc.args[-1]))
if rc != 0:
# and this reflects the command running but failing
if not DEBUG:
cmd = executable
raise DistutilsExecError(
"command %r failed with exit status %d" % (cmd, rc))
if sys.platform == 'darwin':
from distutils import sysconfig
_cfg_target = None
_cfg_target_split = None
def _spawn_posix(cmd, search_path=1, verbose=0, dry_run=0):' '.join(cmd))
if dry_run:
executable = cmd[0]
exec_fn = search_path and os.execvp or os.execv
env = None
if sys.platform == 'darwin':
global _cfg_target, _cfg_target_split
if _cfg_target is None:
_cfg_target = sysconfig.get_config_var(
if _cfg_target:
_cfg_target_split = [int(x) for x in _cfg_target.split('.')]
if _cfg_target:
# ensure that the deployment target of build process is not less
# than that used when the interpreter was built. This ensures
# extension modules are built with correct compatibility values
cur_target = os.environ.get('MACOSX_DEPLOYMENT_TARGET', _cfg_target)
if _cfg_target_split > [int(x) for x in cur_target.split('.')]:
my_msg = ('$MACOSX_DEPLOYMENT_TARGET mismatch: '
'now "%s" but "%s" during configure'
% (cur_target, _cfg_target))
raise DistutilsPlatformError(my_msg)
env = dict(os.environ,
exec_fn = search_path and os.execvpe or os.execve
pid = os.fork()
if pid == 0: # in the child
if env is None:
exec_fn(executable, cmd)
exec_fn(executable, cmd, env)
except OSError as e:
if not DEBUG:
cmd = executable
sys.stderr.write("unable to execute %r: %s\n"
% (cmd, e.strerror))
if not DEBUG:
cmd = executable
sys.stderr.write("unable to execute %r for unknown reasons" % cmd)
else: # in the parent
# Loop until the child either exits or is terminated by a signal
# (ie. keep waiting if it's merely stopped)
while True:
pid, status = os.waitpid(pid, 0)
except OSError as exc:
if not DEBUG:
cmd = executable
raise DistutilsExecError(
"command %r failed: %s" % (cmd, exc.args[-1]))
if os.WIFSIGNALED(status):
if not DEBUG:
cmd = executable
raise DistutilsExecError(
"command %r terminated by signal %d"
% (cmd, os.WTERMSIG(status)))
elif os.WIFEXITED(status):
exit_status = os.WEXITSTATUS(status)
if exit_status == 0:
return # hey, it succeeded!
if not DEBUG:
cmd = executable
raise DistutilsExecError(
"command %r failed with exit status %d"
% (cmd, exit_status))
elif os.WIFSTOPPED(status):
if not DEBUG:
cmd = executable
raise DistutilsExecError(
"unknown error executing %r: termination status %d"
% (cmd, status))
def find_executable(executable, path=None):
"""Tries to find 'executable' in the directories listed in 'path'.
A string listing directories separated by 'os.pathsep'; defaults to
os.environ['PATH']. Returns the complete filename or None if not found.
_, ext = os.path.splitext(executable)
if (sys.platform == 'win32') and (ext != '.exe'):
executable = executable + '.exe'
if os.path.isfile(executable):
return executable
if path is None:
path = os.environ.get('PATH', None)
if path is None:
path = os.confstr("CS_PATH")
except (AttributeError, ValueError):
# os.confstr() or CS_PATH is not available
path = os.defpath
# bpo-35755: Don't use os.defpath if the PATH environment variable is
# set to an empty string
# PATH='' doesn't match, whereas PATH=':' looks in the current directory
if not path:
return None
paths = path.split(os.pathsep)
for p in paths:
f = os.path.join(p, executable)
if os.path.isfile(f):
# the file exists, we have a shot at spawn working
return f
return None
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