Re: [libgpiod] [RFC PATCH] bindings: python: allow specifying infinite timeout

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Fri, May 19, 2023 at 7:47 PM Nicolas Frattaroli
<frattaroli.nicolas@xxxxxxxxx> wrote:
>
> So far, libgpiod's Python bindings had no way to state that a
> user wishes to wait for events indefinitely, as a timeout of
> None would intentionally be converted to 0 seconds, i.e. return
> from the select call in poll_fd immediately.
>
> The usual Python convention and even the select convention is
> to block indefinitely on a timeout=None. However, changing the
> poll_fd function to do this now would change an (intentional)
> API design choice by libgpiod 2.0 that API users presumably
> rely on.
>
> By allowing float("inf") (or in fact math.inf, or your favourite
> other way to get an infinite float) to mean waiting infinitely
> solves this by extending the API rather than changing it.
>
> On gpiod Python bindings without this change, passing inf results
> in an OverflowError being raised in select. API users who wish to
> support older versions of the bindings can catch this exception and
> act on it.
>
> Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@xxxxxxxxx>
> ---
>  bindings/python/gpiod/chip.py         | 3 ++-
>  bindings/python/gpiod/internal.py     | 4 ++++
>  bindings/python/gpiod/line_request.py | 3 ++-
>  3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/bindings/python/gpiod/chip.py b/bindings/python/gpiod/chip.py
> index 97ff340..95c5757 100644
> --- a/bindings/python/gpiod/chip.py
> +++ b/bindings/python/gpiod/chip.py
> @@ -195,7 +195,8 @@ class Chip:
>          Args:
>            timeout:
>              Wait time limit represented as either a datetime.timedelta object
> -            or the number of seconds stored in a float.
> +            or the number of seconds stored in a float. A timeout of None
> +            returns immediately, use float("inf") to wait indefinitely.
>
>          Returns:
>            True if an info event is ready to be read from the chip, False if the
> diff --git a/bindings/python/gpiod/internal.py b/bindings/python/gpiod/internal.py
> index 37e8b62..141cfe9 100644
> --- a/bindings/python/gpiod/internal.py
> +++ b/bindings/python/gpiod/internal.py
> @@ -2,6 +2,7 @@
>  # SPDX-FileCopyrightText: 2022 Bartosz Golaszewski <brgl@xxxxxxxx>
>
>  from datetime import timedelta
> +from math import inf
>  from select import select
>  from typing import Optional, Union
>
> @@ -15,5 +16,8 @@ def poll_fd(fd: int, timeout: Optional[Union[timedelta, float]] = None) -> bool:
>      else:
>          sec = timeout
>
> +    if sec == inf:
> +        sec = None
> +
>      readable, _, _ = select([fd], [], [], sec)
>      return True if fd in readable else False
> diff --git a/bindings/python/gpiod/line_request.py b/bindings/python/gpiod/line_request.py
> index a0f97b7..ae21835 100644
> --- a/bindings/python/gpiod/line_request.py
> +++ b/bindings/python/gpiod/line_request.py
> @@ -178,7 +178,8 @@ class LineRequest:
>          Args:
>            timeout:
>              Wait time limit expressed as either a datetime.timedelta object
> -            or the number of seconds stored in a float.
> +            or the number of seconds stored in a float. None returns
> +            immediately. Use float("inf") to wait indefinitely.
>
>          Returns:
>            True if events are ready to be read. False on timeout.
> --
> 2.40.1
>

I like this approach too. In fact - it may be even clearer and more
intuitive than converting None to infinite timeout.

Any objections against using negative numbers for the same purpose as well?

Bart