Python Virtual Machine Reference
mwh at python.net
Thu Feb 19 12:29:30 CET 2004
Jeff Epler <jepler at unpythonic.net> writes:
> On Wed, Feb 18, 2004 at 10:20:37PM +0000, Dave Kuhlman wrote:
> > But, I don't understand what the connection is between the AST
> > (abstract syntax tree) and the byte code interpreter's op-codes.
> > Maybe someone else can explain that. Perhaps the real Python
> > compiler does not use the AST.
> The parser transforms the string of tokens into an AST, and then
> generates bytecode by traversing the AST. After bytecode generation,
> the AST is discarded.
Which AST are we talking about here?
Python's built in parser produces an exceedingly concrete syntax tree
(ECST? :-). This is the input to the builtin compiler
(Python/compile.c). The Lib/compiler package translates the ECST into
a more genuine AST, and then walks over *that* to generate bytecode.
(The docs for the builtin parser module occasionally refer to the ECST
as an AST, but that's basically a lie).
What happens on the ast-branch (the "new compiler" branch), I'm not so
sure about. An AST (AFAIK different from Lib/compiler's) is involved
somewhere, but I'm not sure how it's produced.
Finding a needle in a haystack is a lot easier if you burn down
the haystack and scan the ashes with a metal detector.
-- the Silicon Valley Tarot (another one nicked from David Rush)
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