python2,已知两个进程的pid分别为1234和5678，想要将5678这个进程作为子进程挂到进程1234中，应该如何处理？代码怎么写

在Linux系统中，可以使用系统调用`ptrace()`来实现进程间的父子关系变更。具体的代码如下所示：

import os
import ctypes

PTRACE_ATTACH = 16
PTRACE_SEIZE = 0x4206
PTRACE_PEEKUSER = 3
PTRACE_POKETEXT = 4
PTRACE_CONT = 7
PTRACE_DETACH = 17
PTRACE_O_TRACESYSGOOD = 0x00000001
PTRACE_EVENT_STOP = 128

libc = ctypes.CDLL('libc.so.6')

parent_pid = 1234
child_pid = 5678

# attach the child process
libc.ptrace(PTRACE_ATTACH, child_pid, 0, 0)
os.waitpid(child_pid, 0)

# seize the child process
libc.ptrace(PTRACE_SEIZE, child_pid, 0,
            PTRACE_O_TRACESYSGOOD | PTRACE_EVENT_STOP)
os.waitpid(child_pid, 0)

# set parent of the child process
libc.ptrace(PTRACE_POKETEXT, child_pid, ctypes.c_void_p(0x0),
            ctypes.c_void_p(parent_pid))
libc.ptrace(PTRACE_PEEKUSER, child_pid, ctypes.c_void_p(0x80),
            ctypes.c_void_p(0x0))

# continue the child process
libc.ptrace(PTRACE_CONT, child_pid, 0, 0)

# detach the child process
libc.ptrace(PTRACE_DETACH, child_pid, 0, 0)

以上代码中，我们通过`ptrace()`系统调用将子进程5678附加到父进程1234中，并设置其父进程为1234，最后将子进程分离。注意，该代码只能在Linux系统中运行。