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From: John Nagle on 23 Jun 2010 12:10
'_sre.SRE_Pattern' is what "re.compile" returns.

Is that a mutable object, with state that changes
during the parse, or is it an immutable constant? Can
two threads use the same '_sre.SRE_Pattern' at the same time?

(I'm writing something to find race conditions in existing code,
which is why all these obscure introspection-related questions.)

John Nagle
From: Stephen Hansen on 23 Jun 2010 13:27
On Jun 23, 2010, at 9:10 AM, John Nagle <nagle(a)animats.com> wrote:

> '_sre.SRE_Pattern' is what "re.compile" returns.
>
> Is that a mutable object, with state that changes
> during the parse, or is it an immutable constant? Can
> two threads use the same '_sre.SRE_Pattern' at the same time?

Ouch. I hope it is thread safe or I have some problems. But: since
compiled regular expressions are automatically cached and used when
one throws non compiled expressions into re, ISTM they have to be
thread safe. Or we'd have tons of problems.

--Stephen via iPad.
From: MRAB on 23 Jun 2010 13:40
John Nagle wrote:
> '_sre.SRE_Pattern' is what "re.compile" returns.
>
> Is that a mutable object, with state that changes
> during the parse, or is it an immutable constant? Can
> two threads use the same '_sre.SRE_Pattern' at the same time?
>
> (I'm writing something to find race conditions in existing code,
> which is why all these obscure introspection-related questions.)
>
A compiled pattern instance is immutable and threadsafe.

BTW, its methods don't release the GIL, so even if it wasn't threadsafe,
it would still be safe. :-)
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