6.1.5 Process Management

These functions may be used to create and manage additional processes.

execl (path, arg0, arg1, ...): This is equivalent to "execv(path, (arg0, arg1, ...))". Availability: Unix, Windows.

execle (path, arg0, arg1, ..., env): This is equivalent to "execve(path, (arg0, arg1, ...), env)". Availability: Unix, Windows.

execlp (path, arg0, arg1, ...): This is equivalent to "execvp(path, (arg0, arg1, ...))". Availability: Unix, Windows.

execv (path, args): Execute the executable path with argument list args, replacing the current process (i.e., the Python interpreter). The argument list may be a tuple or list of strings. Availability: Unix, Windows.

execve (path, args, env): Execute the executable path with argument list args, and environment env, replacing the current process (i.e., the Python interpreter). The argument list may be a tuple or list of strings. The environment must be a dictionary mapping strings to strings. Availability: Unix, Windows.

execvp (path, args): This is like "execv(path, args)" but duplicates the shell's actions in searching for an executable file in a list of directories. The directory list is obtained from environ['PATH']. Availability: Unix, Windows.

execvpe (path, args, env): This is a cross between execve() and execvp(). The directory list is obtained from env['PATH']. Availability: Unix, Windows.

_exit (n): Exit to the system with status n, without calling cleanup handlers, flushing stdio buffers, etc. Availability: Unix, Windows.
Note: the standard way to exit is sys.exit(n). _exit() should normally only be used in the child process after a fork().

fork (): Fork a child process. Return 0 in the child, the child's process id in the parent. Availability: Unix.

kill (pid, sig): Kill the process pid with signal sig. Availability: Unix.

nice (increment): Add increment to the process's ``niceness''. Return the new niceness. Availability: Unix.

plock (op): Lock program segments into memory. The value of op (defined in <sys/lock.h>) determines which segments are locked. Availability: Unix.

spawnv (mode, path, args): Execute the program path in a new process, passing the arguments specified in args as command-line parameters. args may be a list or a tuple. mode is a magic operational constant. See the Visual C++ Runtime Library documentation for further information; the constants are exposed to the Python programmer as listed below. Availability: Windows. New in version 1.5.2.

spawnve (mode, path, args, env): Execute the program path in a new process, passing the arguments specified in args as command-line parameters and the contents of the mapping env as the environment. args may be a list or a tuple. mode is a magic operational constant. See the Visual C++ Runtime Library documentation for further information; the constants are exposed to the Python programmer as listed below. Availability: Windows. New in version 1.5.2.

P_WAIT
P_NOWAIT
P_NOWAITO
P_OVERLAY
P_DETACH: Possible values for the mode parameter to spawnv() and spawnve(). Availability: Windows. New in version 1.5.2.

system (command): Execute the command (a string) in a subshell. This is implemented by calling the Standard C function system(), and has the same limitations. Changes to posix.environ, sys.stdin, etc. are not reflected in the environment of the executed command. The return value is the exit status of the process encoded in the format specified for wait(), except on Windows 95 and 98, where it is always 0. Note that POSIX does not specify the meaning of the return value of the C system() function, so the return value of the Python function is system-dependent. Availability: Unix, Windows.

times (): Return a 5-tuple of floating point numbers indicating accumulated (CPU or other) times, in seconds. The items are: user time, system time, children's user time, children's system time, and elapsed real time since a fixed point in the past, in that order. See the Unix manual page times(2) or the corresponding Windows Platform API documentation. Availability: Unix, Windows.

wait (): Wait for completion of a child process, and return a tuple containing its pid and exit status indication: a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero); the high bit of the low byte is set if a core file was produced. Availability: Unix.

waitpid (pid, options): Wait for completion of a child process given by process id pid, and return a tuple containing its process id and exit status indication (encoded as for wait()). The semantics of the call are affected by the value of the integer options, which should be 0 for normal operation. Availability: Unix.
If pid is greater than 0, waitpid() requests status information for that specific process. If pid is 0, the request is for the status of any child in the process group of the current process. If pid is -1, the request pertains to any child of the current process. If pid is less than -1, status is requested for any process in the process group -pid (the absolute value of pid).

WNOHANG: The option for waitpid() to avoid hanging if no child process status is available immediately. Availability: Unix.

The following functions take a process status code as returned by system(), wait(), or waitpid() as a parameter. They may be used to determine the disposition of a process.

WIFSTOPPED (status): Return true if the process has been stopped. Availability: Unix.

WIFSIGNALED (status): Return true if the process exited due to a signal. Availability: Unix.

WIFEXITED (status): Return true if the process exited using the exit(2) system call. Availability: Unix.

WEXITSTATUS (status): If WIFEXITED(status) is true, return the integer parameter to the exit(2) system call. Otherwise, the return value is meaningless. Availability: Unix.

WSTOPSIG (status): Return the signal which caused the process to stop. Availability: Unix.

WTERMSIG (status): Return the signal which caused the process to exit. Availability: Unix.

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