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The goal of this patch to keep people doing silly things like producing a Try with no finalbody or excepthandlers and segfaulting the compiler in unpleasant ways.

I see what you did there :P

2011年7月16日 Armin Ronacher <report@bugs.python.org>:
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> Armin Ronacher <armin.ronacher@active-4.com> added the comment:
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> I see what you did there :P
Is that a message of approval? :)

From a top level view, the patch adds PyAST_Validate (with helpers) to ast.c and one call to PyAST_Validate in bltinmodule.c in builtin_compile(). The added tests do every silly thing you can think of.
Does PyAST_Validate get invoked for all calls to compile() or just those with an ast as input. To put it another way, does it validate *all* asts, including those generated by the code parser, or just user-constructed asts. If just the latter now, it seems that turning it on for parser asts at least temporarily could test that it does not invalidate valid code and could be used to test an ast-level optimizer.
Two obvious questions: 1) does this address a real problem that has happened in the field or something that just *might* happen; 2) what is the time penalty (compared to the time of compilation). I guess these amount to "Is the maintenance burden on developers and speed burden on users worth the benefit?". In theory, I am in favor of anything that prevents segfaults. Would that ctypes use could be similarly validated (yes, this is a joke;-).
A last question, whose answer might depend on those above: given that the new function is not exposed to users, why not validate as part of compilation, to avoid walking the tree twice?

1) Yes, it address a real concern that arose during Armin's GSOC project which has been developing a unified template compilation architecture (via the AST module) for Django and Jinja2.
2) Asking speed questions about this is silly IMO, if compiling functions is your bottleneck, your application design is very very broken.

It'd be nice to get this in soon, so phase 2 can begin.

New changeset 4090dfdf91a4 by Benjamin Peterson in branch 'default':
add a AST validator (closes #12575)
http://hg.python.org/cpython/rev/4090dfdf91a4 

New changeset eec8e61992fb654d4cf58de4d727c18622b8303e by Victor Stinner in branch 'master':
bpo-43244: Remove the PyAST_Validate() function (GH-24911)
https://github.com/python/cpython/commit/eec8e61992fb654d4cf58de4d727c18622b8303e