Atoms, Identifiers, and Primaries

[Dave Angel]

On 04/16/2013 10:57 PM, Bruce McGoveran wrote:
> These are terms that appear in section 5 (Expressions) of the Python online documentation.  I'm having some trouble understanding what, precisely, these terms mean.  I'd appreciate the forum's thoughts on these questions:
>
>
> 3.  Section 5.3.1 offers this definition of an attributeref:
>      attributeref ::= primary "." identifier
>
> Now, I was at first a little concerned to see the non-terminal primary on the right hand side of the definition, since primary is defined to include attributeref in section 5.3 (so this struck me as circular).  Am I correct in thinking attributeref is defined this way to allow for situations in which the primary, whether an atom, attributeref (example:  an object on which a method is called that returns another object), subscription, slicing, or call, returns an object with property identifier?
>

It is circular.  Nothing wrong with that.  It means that not only can 
you use
     a.b

but also
     a.b.c

and
     a.b.c.d.e.f.g

without any explicit limit.  if a non-circular definition were to be 
attempted, you might need a few dozen rules, just to cover what someone 
*might* happen to use in an expression.  Of course normally, one doesn't 
go much beyond a.b.c in a single expression.


-- 
DaveA