Python-python中如何知道subprocess在等待输入？

Question

sp.py:

#!/usr/bin/env python3
s = input('Waiting for your input:')
print('Data:' + s)

Answer 1

 import subprocess as sp
pobj = sp.Popen('sp.py',stdin=sp.PIPE,stdout=sp.PIPE,shell=True)
print(pobj.stdout.read().decode())#阻塞在这里~~
pobj.stdin.write(b'something...')
print(pobj.stdout.read().decode())

修改为

 import subprocess as sp
pobj = sp.Popen('sp.py',stdin=sp.PIPE,stdout=sp.PIPE,shell=True)
stdout, stderr = pobj.communicate(b'something...')
print(stdout.decode())

关于如何知道subprocess在等待输入？我没能找到什么通用的办法，因为写管道总是ready的，无法确定子进程是否阻塞在读标准输入，对于确切的子进程，可以用pexpect 模块猜测并写入参数