Subprocess timeout does not work

I have some buggy OCaml programs in strings, and I am using Python subprocess to check the feedback from the compiler. However, because there are some programs contain infinite loops, subprocess stuck even I set timeout field.

Environment: Windows 10, Python 3.5.1

This is the code I have tried:

annotated_prog = "let rec ww : ('a -> 'a * bool) * 'a -> 'a = fun (f,b)  ->  let (b',c') = f b in if c' then ww (f, b') else b';;\n let _ = let f x = let xx = (x * x) * x in (xx, (xx < 100)) in ww (f, 1);;"

try:
error_output = subprocess.run(["ocaml"], input = annotated_prog, 
                         stdout=subprocess.PIPE,universal_newlines = True, timeout=1)

except TimeoutExpired:
  error_output = None

However, the code still goes to infinite loop and cannot work.

Another way I have tried:

def run(cmd, timeout_sec):
  proc = subprocess.Popen(["ocaml"], stdout=subprocess.PIPE, 
         stderr=subprocess.PIPE,universal_newlines = True)
  proc.communicate(timeout = timeout_sec)       
  print(proc.communicate("let a = b;;\n")[0])

This doesn't even give a correct output:

what I expect: Characters 8-9: Error: Unbound value b

what I got: OCaml version 4.02.3

In this way how can I even get the correct output from python?

def run(timeout_sec):
  proc = subprocess.Popen(["python"], stdout=subprocess.PIPE, 
  stderr=subprocess.PIPE,universal_newlines = True)
  print(cmd)
  print(proc.communicate("while True: print('hello')\n", timeout = timeout_sec)[0])

try:
      error_output =run(1)
except subprocess.TimeoutExpired:
      print('timeout')

print('error_output')

What I expect: 'time out' with or w/o a bunch of hellos What I got: None