prompt doesn't show in docker image (2.0 branch)

I was trying to run my application on a python docker container but the prompt is not shown. Here is a simple way to reproduce it.

docker pull python
docker run --name python -dit python
docker exec -it python /bin/bash

then in the container, install prompt_toolkit

pip install git+https://github.com/jonathanslenders/python-prompt-toolkit

a simple script test.py

from prompt_toolkit import prompt

print("enter something")
text = prompt("> ")
print("you entered %s." % text)

run the script and enter "foo"

root@2084abd7fdb1:/# python test.py
enter something
you entered foo.

Note that the prompt was not shown in above.
Interestingly, it works again if I reset the terminal

root@2084abd7fdb1:/# reset
root@2084abd7fdb1:/# python test.py
enter something
> bar
you entered bar.

BTW, I am using macOS iTerm if it matters.

Start by reproducing the issue with the listed Docker commands, prompt_toolkit installation, and test.py entry point, both before and after running reset. The payload names no source file or test; trace the prompt path responsible for terminal display. Done means the prompt is visible in the reported container scenario without requiring reset.