[Python-Dev] [IronPython] Exception for setting attributes of built-in type (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Mon Jun 15 19:20:41 CEST 2009

Guido van Rossum wrote:

On Mon, Jun 15, 2009 at 9:10 AM, Michael Foord<fuzzyman at voidspace.org.uk> wrote:

Dino Viehland wrote:

Guido wrote:

I should add that this policy is also forced somewhat by the existence of the "multiple interpreters in one address space" feature, which is used e.g. by modpython. This feature attempts to provide isolation between interpreters to the point that each one can have a completely different set of modules loaded and can be working on a totally different application. The implementation of CPython shares built-in types between multiple interpreters (and it wouldn't be easy to change this); if you were able to modify a built-in type from one interpreter, all other interpreters would see that same modification.

IronPython is in the exact same boat here - we share built-in types Across multiple Python engines as well. And indeed it is needed - if you are working with multiple interpreters (engines in IronPython) you don't want isinstance(something, dict) to fail because it is a dictionary from a different interpreter... Ah, but that suggests you have sharing between different interpreters. If you're doing that, perhaps you shouldn't be using multiple interpreters, but instead multiple threads? Well, in our use case we use multiple engines to provide an isolated execution context for every document (the Resolver One spreadsheet written in IronPython). Each of these has their own calculation thread as well - but the engine per document structure is nice and clean and means each document can have its own set of modules loaded without affecting the other documents (although they share a core set of modules).

Once we move these engines into their own app domains we can completely isolate each document and apply separate security permissions to each one. That might mean each document effectively paying the not-insubstantial startup time hit and we haven't begun to look at how to mitigate that.

Michael

-- http://www.ironpythoninaction.com/ http://www.voidspace.org.uk/blog

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