I suggest to reopen this issue as there was a regression with python3.

import sys
sys.stdin = open("/dev/tty", "r")
import readline
print(input())

Write some text and press left.
Expected: the cursor goes left.
Actual: prints '^[[D' as is readline had not been imported.

bltinmodule.c checks that the current sys.stdin filno matches the C stdin fileno. When they are different, it falls back to the default input implementation.

https://github.com/python/cpython/blob/1e7b858575d0ad782939f86aae4a2fa1c29e9f14/Python/bltinmodule.c#L2097

I noticed that PyFile_AsFile no longer exists. Would calling `fdopen` be acceptable?