[Python-Dev] Re: Another test_compiler mystery (original) (raw)

Michael Hudson mwh at python.net
Thu Aug 12 12:33:48 CEST 2004

Tim Peters <tim.peters at gmail.com> writes:

Here's some puzzling evidence (WinXP Pro SP1). The test driver, for convenience:

""" import compiler, sys f = open('../Lib/test/testparser.py') guts = f.read() f.close() def ouch(n): if n == 0: return compiler.compile(guts, "", "exec") else: return ouch(n-1) for n in range(0, 50): try: ouch(n) msg = 'ok' except KeyboardInterrupt: raise except Exception, msg: msg = str(sys.excinfo()[0]) + ' ' + str(msg) print n, msg """ The loop starts at 0 this time, and I'm only looking at a debug-build Python. The stack size for an .exe can be specified to 4-byte granularity. Here's the largest stack size at which that produces no output at all: C:\Code\python\PCbuild>editbin /stack:1310720 pythond.exe Microsoft (R) COFF Binary File Editor Version 6.00.8447 Copyright (C) Microsoft Corp 1992-1998. All rights reserved. C:\Code\python\PCbuild>pythond temp.py C:\Code\python\PCbuild>echo %ERRORLEVEL% 128

Add 4 measly bytes, and it's a world of difference: C:\Code\python\PCbuild>editbin /stack:1310724 pythond.exe Microsoft (R) COFF Binary File Editor Version 6.00.8447 Copyright (C) Microsoft Corp 1992-1998. All rights reserved.

C:\Code\python\PCbuild>pythond temp.py 0 ok 1 ok ... 41 ok 42 ok C:\Code\python\PCbuild>echo %ERRORLEVEL% 128 So it still vanishes early, but gets thru the entire compiler.compile() business + 42 additional stacked Python calls! That's awfully impressive for four bytes. That suggests "the problem" isn't in detecting Python-level recursion.

Has the failure mode of alloca() changed? I take it you're building with VC++ 7.1? What happens for a VC++ 6 build?

Hmm, a moment with msdn suggests that there's been no significant changes here, although the documentation is for _alloca(), and Python calls alloca(). That can't make any difference, can it?

It still smells like a tool change to me.

Cheers, mwh

-- 58. Fools ignore complexity. Pragmatists suffer it. Some can avoid it. Geniuses remove it. -- Alan Perlis, http://www.cs.yale.edu/homes/perlis-alan/quotes.html

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