[Python-Dev] Assign(expr* targets, expr value) (original) (raw)

Brett Cannon brett at python.org
Fri Nov 22 15:01:32 CET 2013

On Fri, Nov 22, 2013 at 7:29 AM, Benjamin Peterson <benjamin at python.org>wrote:

2013/11/22 anatoly techtonik <techtonik at gmail.com>: > On Fri, Nov 15, 2013 at 5:43 PM, Benjamin Peterson <benjamin at python.org> wrote: >> 2013/11/15 anatoly techtonik <techtonik at gmail.com>: >>> On Tue, Nov 12, 2013 at 5:08 PM, Benjamin Peterson <_ _benjamin at python.org> wrote: >>>> 2013/11/12 anatoly techtonik <techtonik at gmail.com>: >>>>> On Sun, Nov 10, 2013 at 8:34 AM, Benjamin Peterson <_ _benjamin at python.org> wrote: >>>>>> 2013/11/10 anatoly techtonik <techtonik at gmail.com>: >>>>>>> http://hg.python.org/cpython/file/1ee45eb6aab9/Parser/Python.asdl >>>>>>> >>>>>>> In Assign(expr* targets, expr value), why the first argument is a list? >>>>>> >>>>>> x = y = 42 >>>>> >>>>> Thanks. >>>>> >>>>> Speaking of this ASDL. expr* targets means that multiple entities of >>>>> expr under the name 'targets' can be passed to Assign statement. >>>>> Assign uses them as left value. But expr definition contains things >>>>> that can not be used as left side assignment targets: >>>>> >>>>> expr = BoolOp(boolop op, expr* values) >>>>> | BinOp(expr left, operator op, expr right) >>>>> ... >>>>> | Str(string s) -- need to specify raw, unicode, etc? >>>>> | Bytes(bytes s) >>>>> | NameConstant(singleton value) >>>>> | Ellipsis >>>>> >>>>> -- the following expression can appear in assignment context >>>>> | Attribute(expr value, identifier attr, exprcontext ctx) >>>>> | Subscript(expr value, slice slice, exprcontext ctx) >>>>> | Starred(expr value, exprcontext ctx) >>>>> | Name(identifier id, exprcontext ctx) >>>>> | List(expr* elts, exprcontext ctx) >>>>> | Tuple(expr* elts, exprcontext ctx) >>>>> >>>>> If I understand correctly, this is compiled into C struct definitions >>>>> (Python-ast.c), and there is a code to traverse the structure, but >>>>> where is code that validates that the structure is correct? Is it done >>>>> on the first level - text file parsing, before ASDL is built? If so, >>>>> then what is the role of this ADSL exactly that the first step is >>>>> unable to solve? >>>> >>>> Only valid expression targets are allowed during AST construction. See >>>> setexprcontext in ast.c. >>> >>> Oh my. Now there is also CST in addition to AST. This stuff - >>> http://docs.python.org/devguide/ - badly needs diagrams about data >>> transformation toolchain from Python source code to machine >>> execution instructions. I'd like some pretty stuff, but raw blogdiag >>> hack will do the job http://blockdiag.com/en/blockdiag/index.html >>> >>> There is no setexprcontext in my copy of CPython code, which >>> seems to be some alpha of Python 3.4 >> >> It's actually called setcontext. > > Ok. So what is the process? > > SOURCE --> TOKEN STREAM --> SENTENCE STREAM --> CST --> > --> AST --> BYTECODE > > Is that right?

I don't know what sentence stream is, but otherwise looks right.

If you want more of an overview: http://pyvideo.org/video/2331/from-source-to-code-how-cpythons-compiler-works -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20131122/994a2590/attachment.html>

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