2013/11/15 anatoly techtonik <techto...@gmail.com>: > On Tue, Nov 12, 2013 at 5:08 PM, Benjamin Peterson <benja...@python.org> > wrote: >> 2013/11/12 anatoly techtonik <techto...@gmail.com>: >>> On Sun, Nov 10, 2013 at 8:34 AM, Benjamin Peterson <benja...@python.org> >>> wrote: >>>> 2013/11/10 anatoly techtonik <techto...@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, expr_context ctx) >>> | Subscript(expr value, slice slice, expr_context ctx) >>> | Starred(expr value, expr_context ctx) >>> | Name(identifier id, expr_context ctx) >>> | List(expr* elts, expr_context ctx) >>> | Tuple(expr* elts, expr_context 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 >> set_expr_context 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 set_expr_context in my copy of CPython code, which > seems to be some alpha of Python 3.4
It's actually called set_context. > >>> Is it possible to fix ADSL to move `expr` that are allowed in Assign >>> into `expr` subset? What effect will it achieve? I mean - will ADSL >>> compiler complain about wrong stuff on the left side, or it will still >>> be a role of some other component. Which one? >> >> I'm not sure what you mean by an `expr` subset. > > Transform this: > > 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, expr_context ctx) > | Subscript(expr value, slice slice, expr_context ctx) > | Starred(expr value, expr_context ctx) > | Name(identifier id, expr_context ctx) > | List(expr* elts, expr_context ctx) > | Tuple(expr* elts, expr_context ctx) > > to this: > > 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 > | expr_asgn > > expr_asgn = > Attribute(expr value, identifier attr, expr_context ctx) > | Subscript(expr value, slice slice, expr_context ctx) > | Starred(expr value, expr_context ctx) > | Name(identifier id, expr_context ctx) > | List(expr* elts, expr_context ctx) > | Tuple(expr* elts, expr_context ctx) I doubt ASDL will let you do that. -- Regards, Benjamin _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
