Python multiprocessing stdin input

When you take a look at Pythons implementation of multiprocessing.Process._bootstrap() you will see this:

if sys.stdin is not None:
    try:
        sys.stdin.close()
        sys.stdin = open(os.devnull)
    except (OSError, ValueError):
        pass

You can also confirm this by using:

>>> import sys
>>> import multiprocessing
>>> def func():
...     print(sys.stdin)
... 
>>> p = multiprocessing.Process(target=func)
>>> p.start()
>>> <_io.TextIOWrapper name="/dev/null" mode="r" encoding='UTF-8'>

And reading from os.devnull immediately returns empty result:

>>> import os
>>> f = open(os.devnull)
>>> f.read(1)
''

You can work this around by using open(0):

file is either a string or bytes object giving the pathname (absolute or relative to the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.)

And “0 file descriptor“:

File descriptors are small integers corresponding to a file that has been opened by the current process. For example, standard input is usually file descriptor 0, standard output is 1, and standard error is 2:

>>> def func():
...     sys.stdin = open(0)
...     print(sys.stdin)
...     c = sys.stdin.read(1)
...     print('Got', c)
... 
>>> multiprocessing.Process(target=func).start()
>>> <_io.TextIOWrapper name=0 mode="r" encoding='UTF-8'>
Got a