An example of reopening the controlling terminal when stdin is attached to a pipe.

reopen-stdin.py

#!/usr/bin/env python3

"""
An example of re-opening stdin. Lets you pipe input to a program and still interact with
the program via stdin.

Example:

    $ seq 5 | ./reopen-stdin.py
    Type a prefix: #=>
    #=> 1
    #=> 2
    #=> 3
    #=> 4
    #=> 5
"""

import os
import sys

# Duplicate the stdin's file descriptor:
# (You probably want to check whether stdin is a tty first)
pipe_in_fd = os.dup(sys.stdin.fileno())
pipe_in = os.fdopen(pipe_in_fd, "rt")

# Okay, we're done with the pipe:
sys.stdin.close()

# Re-open the controlling terminal using /dev/tty.
# See https://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap10.html
sys.stdin = open("/dev/tty", "rt")

# Getting input from (the new) stdin:
prefix = input("Type a prefix: ").strip()

for line in pipe_in:
    print(prefix, line, end="")