[Python-checkins] CVS: python/nondist/peps pep-0201.txt,1.4,1.5

[Barry Warsaw]

Update of /cvsroot/python/python/nondist/peps
In directory slayer.i.sourceforge.net:/tmp/cvs-serv12662

Modified Files:
	pep-0201.txt 
Log Message:
In a compromise with JHy, and to be more consistent with the style now
documented in PEP1, remove the Emacs page breaks.

Also, Owner: -> Author:, added Created: and Post-History: headers

Changed "Standard For-Loops" section to "Motivation" and shortened
considerably; readers already know how for-loops work in Python.

Added notes about Guido's veto of lazy evaluation.


Index: pep-0201.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0201.txt,v
retrieving revision 1.4
retrieving revision 1.5
diff -C2 -r1.4 -r1.5
*** pep-0201.txt	2000/07/24 17:40:00	1.4
--- pep-0201.txt	2000/07/25 21:51:55	1.5
***************
*** 2,11 ****
  Title: Parallel Iteration
  Version: $Revision$
! Owner: bwarsaw@beopen.com (Barry A. Warsaw)
  Python-Version: 2.0
  Status: Draft
  
  
- 
  Introduction
  
--- 2,12 ----
  Title: Parallel Iteration
  Version: $Revision$
! Author: bwarsaw@beopen.com (Barry A. Warsaw)
  Python-Version: 2.0
  Status: Draft
+ Created: 13-Jul-2000
+ Post-History:
  
  
  Introduction
  
***************
*** 20,59 ****
  
  
! 
! Standard For-Loops
  
!     Motivation for this feature has its roots in a concept described
!     as `parallel for loops'.  A standard for-loop in Python iterates
!     over every element in the sequence until the sequence is
!     exhausted.  A `break' statement inside the loop suite causes an
!     explicit loop exit.  For-loops also have else: clauses which get
!     executed when the loop exits normally (i.e. not by execution of a
!     break).
! 
!     For-loops can iterate over built-in types such as lists and
!     tuples, but they can also iterate over instance types that conform
!     to an informal sequence protocol.  This protocol states that the
!     instance should implement the __getitem__() method, expecting a
!     monotonically increasing index starting at 0, and this method
!     should raise an IndexError when the sequence is exhausted.  This
!     protocol is currently undocumented -- a defect in Python's
!     documentation hopefully soon corrected.
  
-     For-loops are described in the Python language reference
-     manual[1].
  
-     An example for-loop:
- 
-     >>> for i in (1, 2, 3): print i
-     ... 
-     1
-     2
-     3
- 
-     In this example, the variable `i' is called the `target', and is
-     assigned the next element of the list, each time through the loop.
- 
- 
- 
  Parallel For-Loops
  
--- 21,37 ----
  
  
! Motivation
  
!     Standard for-loops in Python iterate over every element in a
!     sequence until the sequence is exhausted[1].  However, for-loops
!     iterate over only a single sequence, and it is often desirable to
!     loop over more than one sequence, in a lock-step, "Chinese Menu"
!     type of way.
! 
!     The common idioms used to accomplish this are unintuitive and
!     inflexible.  This PEP proposes a standard way of performing such
!     iterations by introducing a new builtin function called `zip'.
  
  
  Parallel For-Loops
  
***************
*** 71,80 ****
      (2, 5)
      (3, 6)
- 
-     Here, map() returns a list of N-tuples, where N is the number of
-     sequences in map()'s argument list (after the initial `None').
-     Each tuple is constructed of the i-th elements from each of the
-     argument lists, specifically in this example:
- 
      >>> map(None, a, b)
      [(1, 4), (2, 5), (3, 6)]
--- 49,52 ----
***************
*** 107,111 ****
  
  
- 
  The Proposed Solution
  
--- 79,82 ----
***************
*** 130,134 ****
  
  
- 
  Lazy Execution
  
--- 101,104 ----
***************
*** 139,144 ****
      on demand.
  
  
! 
  Examples
  
--- 109,115 ----
      on demand.
  
+     Guido is strongly opposed to lazy execution.  See Open Issues.
  
! 
  Examples
  
***************
*** 195,199 ****
  
  
- 
  Reference Implementation
  
--- 166,169 ----
***************
*** 293,297 ****
  
  
- 
  Rejected Elaborations
  
--- 263,266 ----
***************
*** 353,359 ****
  
  
- 
  Open Issues
  
      - What should "zip(a)" do?  Given
  
--- 322,331 ----
  
  
  Open Issues
  
+     - Guido opposes lazy evaluation for zip().  He believes zip()
+       should return a real list, with an xzip() lazy evaluator added
+       later if necessary.
+ 
      - What should "zip(a)" do?  Given
  
***************
*** 428,432 ****
  
  
- 
  References
  
--- 400,403 ----
***************
*** 436,440 ****
      TBD: URL to python-dev archives
  
- 
  Copyright
  
--- 407,410 ----