Decide how to use `echo_char` in `getpass.fallback_getpass`

[qc-m]

Hello everyone, I am a Chinese high school student. This is my first contribution to cpython on GitHub. If there are any errors, please kindly point them out. Thank you!
I noticed that in the getpass library of Python 3.14, there was a seemingly useless function call in fallback_getpass: _check_echo. This function was originally designed to check if the echo character is valid, but I think this call is redundant because:

1. fallback_getpass is only called when the terminal settings cannot be controlled, and the echo_char parameter actually does not work properly at this time
   2.In a fallback scenario, even if echo_char is provided, password echo control cannot be implemented
   I suggest removing this unnecessary call. Modify the code as follows:

def fallback_getpass(prompt='Password: ', stream=None, *, echo_char=None):
    # remove the function call
    import warnings
    warnings.warn("Can not control echo on the terminal.", GetPassWarning,
                  stacklevel=2)
    if not stream:
        stream = sys.stderr
    print("Warning: Password input may be echoed.", file=stream)
    return _raw_input(prompt, stream, echo_char=echo_char)

By the way,can we make IDLE support getpass?I think it is important for the beginners!

At last,if I say something wrong, please tell me why and forgive me, thank you!

[StanFromIreland]

From my understanding, the _check_echo_char call isn’t redundant. Firstly, it ensures consistent input validation across APIs, and secondly, prevents invalid input from reaching _raw_input. I also don't think performance is of importance here.

[picnixz]

2.In a fallback scenario, even if echo_char is provided, password echo control cannot be implemented

That's not entirely accurate. I agree that with the default setting it's not properly working (so there is indeed a small bug here), but it can be used as follows:

rendered = io.StringIO()
password = getpass.fallback_getpass(stream=rendered, echo_char="a")
print(rendered.getvalue())  # will render "Warning: ...\nPassword: aaa..."

If rendered is the thing that the user actually see, then it's fine (an app could decide to use something that is not the terminal for reading the input).

OTOH, if we leave the defaults, we get something like that:

>>> password = getpass.fallback_getpass(echo_char="*")
Warning: Password input may be echoed.
Password: abc123<ENTER>
******>>> password
>>> password
'abc123'

So if we're using the default output stream, it may be better to just not have an echo_char. In 3.13, we would have had:

>>> password = getpass.fallback_getpass()
Warning: Password input may be echoed.
Password: abc123<ENTER>
>>> password
'abc123'
>>>

[picnixz]

Btw, performance would not be an issue here. The function is very fast. What's concerning is the "messy" output we get with the default fallbacks when using echo_char.