How to get a raised exception from other thread

[Antoon Pardon]

Op 2005-10-17, Alex Martelli schreef <aleaxit at yahoo.com>:
><themightydoyle at gmail.com> wrote:
>
>> Nevermind.  I found a better solution.  I used shared memory to create
>> a keep-alive flag.  I then use the select function with a specified
>> timeout, and recheck the keep-alive flag after each timeout.
>
> Definitely a better architecture.  Anyway, one supported way for a
> thread to raise an exception in a different thread is function
> thread.interrupt_main(), which raises a KeyboardInterrupt in the *main*
> thread (the one thread that's running at the beginning of your program).
>
> There's also a supported, documented function to raise any given
> exception in any existing thread, but it's deliberately NOT directly
> exposed to Python code -- you need a few lines of  C-coded extension (or
> pyrex, ctypes, etc, etc) to get at the functionality.  This small but
> non-null amount of "attrition" was deliberately put there to avoid
> casual overuse of a facility intended only to help in very peculiar
> cases (essentially in debuggers &c, where the thread's code may be buggy
> and fail to check a keep-alive flag correctly...!-).

I find this rather arrogant. It is not up to the developers of python
to decide how the users of python will use the language. If someone
has use of specific functionality he shouldn't be stopped because his
use is outside the intentions of the developers.

Just suppose you are writing a chess program. You let the program
"think" while it is the users move, but this thinking has to be
interrupted and some cleanup has to be made after the users move
has made a lot of this thinking obsolete by his move. Such code
could be mixture of loops and recursion that makes use of a simple
flag to end it all, unpractical. Use of an exception raised from
somewhere else would IMO in this case be an acceptable choice.

Why should the coder of this software have to go through this
deliberate set up attrition, to get at this functionality, just
because it wasn't intented to be used in such a way by the
developers?

As far as I know, pyrex and ctypes weren't intended to get
at the Python/C api. But they didn't create extra hurdles
for those who could use it that way.

-- 
Antoon Pardon