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

[Peter J. Holzer]

On 2017-10-06 08:09, Steve D'Aprano <steve+python at pearwood.info> wrote:
> What are the right ways for a Python script to detect these sorts of
> situations?
>
> (1) Standard input is coming from a pipe;
>
> (2) Stdin is being read from a file;
>
> (3) Stdin is coming from a human at a terminal;
>
> I get these. How did I do?
>
>
> # 1 detect input coming from a pipe.
> import sys
> import os
> from stat import S_ISFIFO
> if S_ISFIFO(os.fstat(0).st_mode):
>     print("Reading from a pipe")
>
>
> # 2 detect input coming from a regular file.
> from stat import S_ISREG
> if S_ISREG(os.fstat(0).st_mode):
>     print("Reading from a file.")
>
> # 3 detect a terminal, hopefully with a human typing at it
> if os.isatty(0):
>     print("Oy noddy, wake up and type something, I'm waiting for you!")

I'd do it the same way.

> I feel a bit weird about using the magic constant 0 here. Is that guaranteed
> to be stdin on all platforms?

It is guaranteed on POSIX compatible OSs. I think it is also guaranteed
on Windows, Don't know about VMS or the IBM OSs.

> Or should I be using sys.stdin.fileno()?

I'm not conviced that this is much more portable: A platform where stdin
doesn't use file descriptor 0 under the hood might not even use simple
integers as file descriptors at all.

        hp


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