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.

pep-0201.txt

@@ -1,12 +1,13 @@
 PEP: 201
 Title: Parallel Iteration
 Version: $Revision$
-Owner: bwarsaw@beopen.com (Barry A. Warsaw)
+Author: bwarsaw@beopen.com (Barry A. Warsaw)
 Python-Version: 2.0
 Status: Draft
+Created: 13-Jul-2000
+Post-History:
 
 
-
 Introduction
 
     This PEP describes the `parallel iteration' proposal for Python
@@ -19,42 +20,19 @@ Introduction
     history of this file contains the definitive historical record.
 
 
-
+Motivation
-Standard For-Loops
 
-    Motivation for this feature has its roots in a concept described
+    Standard for-loops in Python iterate over every element in a
-    as `parallel for loops'.  A standard for-loop in Python iterates
+    sequence until the sequence is exhausted[1].  However, for-loops
-    over every element in the sequence until the sequence is
+    iterate over only a single sequence, and it is often desirable to
-    exhausted.  A `break' statement inside the loop suite causes an
+    loop over more than one sequence, in a lock-step, "Chinese Menu"
-    explicit loop exit.  For-loops also have else: clauses which get
+    type of way.
-    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
+    The common idioms used to accomplish this are unintuitive and
-    tuples, but they can also iterate over instance types that conform
+    inflexible.  This PEP proposes a standard way of performing such
-    to an informal sequence protocol.  This protocol states that the
+    iterations by introducing a new builtin function called `zip'.
-    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
 
     Parallel for-loops are non-nested iterations over two or more
@@ -70,12 +48,6 @@ Parallel For-Loops
     (1, 4)
     (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)]
 
@@ -106,7 +78,6 @@ Parallel For-Loops
     comprehensions' (see pep-0202.txt).
 
 
-
 The Proposed Solution
 
     The proposed solution is to introduce a new built-in sequence
@@ -129,7 +100,6 @@ The Proposed Solution
     Issues below for more discussion.
 
 
-
 Lazy Execution
 
     For performance purposes, zip() does not construct the list of
@@ -138,8 +108,9 @@ Lazy Execution
     for-loop protocol.  This method constructs the individual tuples
     on demand.
 
+    Guido is strongly opposed to lazy execution.  See Open Issues.
+
 
-
 Examples
 
     Here are some examples, based on the reference implementation
@@ -194,7 +165,6 @@ Examples
     not all the same length.
 
 
-
 Reference Implementation
 
     Here is a reference implementation, in Python of the zip()
@@ -292,7 +262,6 @@ Reference Implementation
         return _Zipper(args, kws)
 
 
-
 Rejected Elaborations
 
     Some people have suggested that the user be able to specify the
@@ -352,9 +321,12 @@ Rejected Elaborations
     advantages.
 
 
-
 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
 
       a = (1, 2, 3); zip(a)
@@ -427,7 +399,6 @@ Open Issues
       always override pad if both were given.
 
 
-
 References
 
     [1] http://www.python.org/doc/devel/ref/for.html    
@@ -435,7 +406,6 @@ References
 
     TBD: URL to python-dev archives
 
-
 Copyright
 
     This document has been placed in the public domain.