How does python build its AST

[MonkeeSage]

On Dec 7, 9:50 am, Kay Schluehr <kay.schlu... at gmx.net> wrote:
> On Dec 7, 3:23 pm, MonkeeSage <MonkeeS... at gmail.com> wrote:
>
> > A quick question about how python parses a file into compiled
> > bytecode. Does it parse the whole file into AST first and then compile
> > the AST, or does it build and compile the AST on the fly as it reads
> > expressions? (If the former case, why can't functions be called before
> > their definitions?)
>
> > Thanks,
> > Jordan
>
> Python uses a highly optimized table based LL(1) parser to create a
> syntax tree. In Python 2.5 it transforms the concrete syntax tree
> ( CST ) into an AST before compilation. Before that it compiled the
> CST directly. I'm not sure what you are asking for ( in parentheses )?
> Parser actions or preprocessing the tree? The latter is definitely
> possible and you can build your own compilation machinery using the
> parser module and the compile function.
>
> Kay

Thanks for your reply. You answered my main question. The secondary
question is why is it a NameError to try to use a variable/function
prior to the declaration in a source file, since python has already
seen the declaration on the first pass building the CST/AST? At
compile time, shouldn't it already know about it? (Forgive my
ignorance.)

Regards,
Jordan