Interactive scripts (back on topic for once) [was Re: The "loop and a half"]

[Ben Bacarisse]

Steve D'Aprano <steve+python at pearwood.info> writes:

> On Fri, 6 Oct 2017 09:33 pm, Ben Bacarisse wrote:
>
>> A general solution to the (rather odd) complaint about silent waiting
>> should really check any input fileno to see if a prompt is needed.  You
>> could argue, though, that anyone who's re-arranged a program's input so
>> that some non-zero input fileno is attached to a terminal won't need the
>> prompt!
>
> I'm afraid I don't quite know if I'm understanding you or not.
>
> I think you mean to say I should look at sys.stdin.fileno(), and if it is 0,
> then write a prompt, and if not, just read from stdin (possibly blocking,
> waiting for input).
>
> Is that right?
>
> But aren't there circumstances where fileno 0 isn't attached to a terminal,
> and writing a prompt would be inappropriate?

No.  The point was that other file descriptors might be associated with
a terminal.  I could, for example, switch the input to an interactive
program that interprets command to be done on some data file so that the
supposedly interactive commands come form a file and I type the data at
a terminal.

The second point was anyone doing this probably does not need a hint
about tying something.

But this detail about other inputs opened by the program aside, it seems
to me that what BartC (and others who want this) needs is a beginners
shell that prints a helpful text whenever it starts a program (or
pipeline of programs) with stdin attached to the terminal.  It's not
really something that every individual program should have to tackle.

-- 
Ben.