Is it possible to prefill a input() in Python 3’s Command Line Interface?

If your Python interpreter is linked against GNU readline, input() will use it. In this case, the following should work:

import readline

def input_with_prefill(prompt, text):
    def hook():
        readline.insert_text(text)
        readline.redisplay()
    readline.set_pre_input_hook(hook)
    result = input(prompt)
    readline.set_pre_input_hook()
    return result