On Dec 7, 5:03 pm, MonkeeSage <[EMAIL PROTECTED]> wrote: > On Dec 7, 9:50 am, Kay Schluehr <[EMAIL PROTECTED]> wrote: > > > > > On Dec 7, 3:23 pm, MonkeeSage <[EMAIL PROTECTED]> 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
When the compiler finds a name not being bound in the function scope it supposes the name is global and a LOAD_GLOBAL opcode is created instead of LOAD_FAST ( accessing locals ). Other than the local/ function scope the global ( module level ) scope is dynamic and the compiler can't know whether a name will be present at runtime. Kay -- http://mail.python.org/mailman/listinfo/python-list
