再附加一条，没有换行存在阻塞的情况，要按单个字符读取，存入暂存区自己判断即可
```
import subprocess

p = subprocess.Popen(["python", "a.py"], stdin=subprocess.PIPE, stdout=subprocess.PIPE, universal_newlines=True,
bufsize=1)

stash = ""
while p.poll() is None:
c = p.stdout.read(1)
stash += c
print(c, end='')
if stash == "Value x: ":
print()
print("[bingo]", stash)
stash = ""
p.stdin.write("hello\n")
```


输出

```
Value x:
[bingo] Value x:
x = hello
```