Status of PEP's?

[Greg Ewing]

James_Althoff at i2.com wrote:
> 
> [David Eppstein]
> >
> >   "for" expression ":"
> 
> You might want to think this through a bit more since neither arbitrary
> "expression" nor arbitrary "conditional" is supported in the suggestions
> posted so far.

The official Python grammar currently defines a for-loop
thusly:

  for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]

where 'exprlist' is, confusingly, *not* a list of
general expressions, but of expressions not including
comparisons.

So it seems that the following would work:

  for_stmt: 'for' (exprlist 'in' testlist 
      | exprlist lt_op exprlist lt_op exprlist
      | exprlist gt_op exprlist gt_op exprlist) ':' suite ['else' ':'
suite]

  lt_op: '<' | '<='
  gt_op: '>' | '>='

Later phases of the compiler would be responsible for checking
that the exprlists in the new parts actually contain only one
item each, and that the middle one is a variable.

-- 
Greg Ewing, Computer Science Dept, University of Canterbury,	  
Christchurch, New Zealand
To get my email address, please visit my web page:	  
http://www.cosc.canterbury.ac.nz/~greg