Allow on to be a predicate: typing.Callable[[BaseException], bool]

[dhirschfeld]

I'm dealing with a library where I want to retry an exception only if the message contains a certain string.

I think the most flexible way to support this whilst being backward compatible would be to change the on argument to allow passing in a predicate callable - e.g.:

 on: type[Exception] | tuple[type[Exception], ...] | Callable[[BaseException], bool],

In the retry code you can then create the predicate like:

if isinstance(on, Callable):
    predicate = on
else:
    predicate = lambda exc: isinstance(exc, on)

...and then in _RetryContextIterator pass it through to tenacity as:

        return cls(
            _name=name,
            _args=args,
            _kw=kw,
            _t_kw={
                "retry": _t.retry_if_exception(predicate),
<snip>

xref: https://github.com/jd/tenacity/blob/main/tenacity/retry.py#L62-L78

[estahn]

I think this is reasonable. I would like to retry in case the downstream service started throttling (429's). I understand this is possible with tenacity, but not with stamina due to the above?

[hynek]

I would be open to a PR, but bear in mind I'm leaving for a vacation tomorrow so merging might take some time!

[dhirschfeld]

Enjoy the vacation! 🌴

No rush on this (for me at least). I'll try to find the time to put in a PR. It should be fairly straightforward.... I think!

[hynek]

famous last words? ;)

[hynek]

This has been merged in #70 – thanks to @gsakkis!