File Description Wrappers and REPL Example

fd2repl.py

import subprocess
import os
import time

# Start the Python REPL in interactive mode, with a pipe for stdin and stdout
proc = subprocess.Popen(
    ["python3", "-i"],
    stdin=subprocess.PIPE,
    stdout=subprocess.PIPE,
    stderr=subprocess.STDOUT  # Merge stderr into stdout for simplicity
)

# Get file descriptors
stdin_fd = proc.stdin.fileno()
stdout_fd = proc.stdout.fileno()

# Wrap both FDs with high-level I/O objects
stdin = open(stdin_fd, "w", encoding="utf-8", closefd=False)
stdout = open(stdout_fd, "r", encoding="utf-8", closefd=False)

# Send a command to the REPL
stdin.write("2 + 2\n")
stdin.flush()

# Give it time to respond
time.sleep(0.2)

# Read output
output = []
while True:
    line = stdout.readline()
    if not line.strip():
        break
    output.append(line)
    if ">>>" in line:
        break

print("REPL output:\n", "".join(output))

# Clean up
stdin.write("exit()\n")
stdin.flush()
proc.wait()

# % python3 repl.py
# REPL output:
#  Python 3.11.1 (v3.11.1:a7a450f84a, Dec  6 2022, 15:24:06) [Clang 13.0.0 (clang-1300.0.29.30)] on darwin
# Type "help", "copyright", "credits" or "license" for more information.
# >>> 4