[Python-ideas] If branch merging

Ryan Gonzalez rymg19 at gmail.com
Wed Jun 10 17:12:19 CEST 2015

Maybe it's just me, but nesting_demo.py has several junk characters at the end (^@).

On June 10, 2015 10:06:26 AM CDT, Chris Angelico <rosuav at gmail.com> wrote:
>On Wed, Jun 10, 2015 at 4:17 PM, Chris Angelico <rosuav at gmail.com>
>>> But I think your quick&dirty hack may be worth playing with even if
>it bans this possibility and a few others, and may not be that hard to
>do if you make that decision, so if I were you I'd try that first.
>> Okay. I'll start poking around with CPython and see what I can do.
>Here's a gross, disgusting, brutal hack. It applies only to try/except
>(but can easily be expanded to other places; it's just a matter of
>calling one function at top and bottom), and it currently assumes that
>you're in a function scope (not at top level, not directly in a class;
>methods are supported).
>(Should I create a tracker issue? It's not even at proof-of-concept at
>this point.)
>Here's how it works: As an 'except' block is entered (at compilation
>stage), a new subscope is defined. At the end of the except block,
>after the "e = None; del e" opcodes get added in, the subscope is
>popped off and disposed of. So long as there is a subscope attached to
>the current compilation unit, any name lookups will be redirected
>through it. Finally, when co_varnames is populated, names get
>de-mangled, thus (possibly) making duplicates in the tuple, but more
>importantly, getting tracebacks and such looking correct.
>The subscope is a tiny thing that just says "this name now becomes
>that mangled name", where the mangled name is the original name dot
>something (eg mangle "e" and get back "e.0x12345678"); they're stored
>in a linked list in the current compiler_unit.
>Currently, locals() basically ignores the magic. If there is no
>"regular" name to be shadowed, then it correctly picks up the interior
>one; if there are both forms, I've no idea how it picks which one to
>put into the dictionary, but it certainly can't logically retain both.
>The fact that it manages to not crash and burn is, in my opinion, pure
>luck :)
>Can compiler_nameop() depend on all names being interned? I have a
>full-on PyObject_RichCompareBool() to check for name equality; if
>they're all interned, I could simply do a pointer comparison instead.
>Next plan: Change compiler_comprehension_generator() to use subscopes
>rather than a full nested function, and then do performance testing.
>Currently, this can only have slowed things down. Removing the
>function call overhead from list comps could give that speed back.
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Sent from my Android device with K-9 Mail. Please excuse my brevity.
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