using Python's AST generator for other languages

Benjamin musiccomposition at gmail.com
Fri Jul 11 00:54:27 CEST 2008


On Jul 10, 12:40 pm, eliben <eli... at gmail.com> wrote:
> Hello,
>
> I'm building a parser in Python, and while pondering on the design of
> my ASTs had the idea to see what Python uses. I quickly got to the
> compiler.ast module, and understood it's automatically generated. So I
> went to the source, ast.txt and tools/compiler/astgen.py, where I was
> this unexpected message:
>
> """Generate ast module from specification
>
> This script generates the ast module from a simple specification,
> which makes it easy to accomodate changes in the grammar.  This
> approach would be quite reasonable if the grammar changed often.
> Instead, it is rather complex to generate the appropriate code.  And
> the Node interface has changed more often than the grammar.
> """
>
> Now, to me the design of the AST in Python looks quite elegant,
> especially from the point of view of the AST's user (using Visitors to
> walk the AST). And astgen.py looks like a nice approach to generate
> tons of boilerplate code.
> So, my questions:
> 1) Is the compiler.ast module really employed during the compilation
> of Python into .pyc files ?

No, the comment refers to the builtin _ast module. The compiler
package is a compiler for Python written in Python.

> 2) What is the meaning of the comment in astgen.py ? Are the Python
> maintainers unhappy with the design of the AST ?3

Node, I think, is talking about a node in the parse tree. (AST is
generated from another parse tree.) See PEP 339 for details.

> 3) What other approach would be recommended to generate a very
> detailed AST hierarchy, if the one in astgen.py is dissapointing ?

astgen.py contains things that are specific to writing Python's AST C
code. Have a look at spark.py in the Parser dir. It is what astgen.py
is based on.
>
> Thanks in advance
> Eli




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