(original) (raw)

On Fri, Nov 15, 2013 at 5:43 PM, Benjamin Peterson <benjamin@python.org> wrote:

> 2013/11/15 anatoly techtonik <techtonik@gmail.com>:

>> On Tue, Nov 12, 2013 at 5:08 PM, Benjamin Peterson <benjamin@python.org> wrote:

>>> 2013/11/12 anatoly techtonik <techtonik@gmail.com>:

>>>> On Sun, Nov 10, 2013 at 8:34 AM, Benjamin Peterson <benjamin@python.org> wrote:

>>>>> 2013/11/10 anatoly techtonik <techtonik@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.

Ok. So what is the process?

�SOURCE --> TOKEN STREAM --> SENTENCE STREAM --> CST -->
\--> AST --> BYTECODE

Is that right?

\>>>> 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.

asdl.py �is plain broken - wrong number of arguments passed to
� � � � � � output function
asdl\_c.py worked ok with fixed ASDL and generated - diff attached.
I don't know what to check further - on Windows without Visual Studio.
\--