Integrated many suggestions from c.l.py and others. Nothing

substantial w.r.t. the proposed solution, just clarifications,
additional references, and an explanation of why most syntax changes
don't work.

pep-0201.txt

@@ -10,14 +10,14 @@ Post-History: 27-Jul-2000
 
 Introduction
 
-    This PEP describes the `lockstep iteration' proposal for Python
+    This PEP describes the `lockstep iteration' proposal.  This PEP
-    2.0.  This PEP tracks the status and ownership of this feature,
+    tracks the status and ownership of this feature, slated for
-    slated for introduction in Python 2.0.  It contains a description
+    introduction in Python 2.0.  It contains a description of the
-    of the feature and outlines changes necessary to support the
+    feature and outlines changes necessary to support the feature.
-    feature.  This PEP summarizes discussions held in mailing list
+    This PEP summarizes discussions held in mailing list forums, and
-    forums, and provides URLs for further information, where
+    provides URLs for further information, where appropriate.  The CVS
-    appropriate.  The CVS revision history of this file contains the
+    revision history of this file contains the definitive historical
-    definitive historical record.
+    record.
 
 
 Motivation
@@ -25,13 +25,17 @@ 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"
+    loop over more than one sequence in a lock-step fashion.  In other
-    type of way.
+    words, in a way such that nthe i-th iteration through the loop
+    returns an object containing the i-th element from each sequence.
 
-    The common idioms used to accomplish this are unintuitive and
+    The common idioms used to accomplish this are unintuitive.  This
-    inflexible.  This PEP proposes a standard way of performing such
+    PEP proposes a standard way of performing such iterations by
-    iterations by introducing a new builtin function called `zip'.
+    introducing a new builtin function called `zip'.
 
+    While the primary motivation for zip() comes from lock-step
+    iteration, by implementing zip() as a built-in function, it has
+    additional utility in contexts other than for-loops.
 
 Lockstep For-Loops
 
@@ -70,13 +74,20 @@ Lockstep For-Loops
       [(1, 4), (2, 5), (3, 6), (None, 7)]
 
     For these reasons, several proposals were floated in the Python
-    2.0 beta time frame for providing a better spelling of lockstep
+    2.0 beta time frame for syntactic support of lockstep for-loops.
-    for-loops.  The initial proposals centered around syntactic
+    Here are two suggestions:
-    changes to the for statement, but conflicts and problems with the
-    syntax were unresolvable, especially when lockstep for-loops were
-    combined with another proposed feature called `list
-    comprehensions' (see pep-0202.txt).
 
+    for x in seq1, y in seq2:
+        # stuff
+
+    for x, y in seq1, seq2:
+        # stuff
+
+    Neither of these forms would work, since they both already mean
+    something in Python and changing the meanings would break existing
+    code.  All other suggestions for new syntax suffered the same
+    problem, or were in conflict with other another proposed feature
+    called `list comprehensions' (see pep-0202.txt).
 
 The Proposed Solution
 
@@ -206,7 +217,8 @@ References
     [1] http://www.python.org/doc/current/ref/for.html
     [2] http://www.haskell.org/onlinereport/standard-prelude.html#$vzip
 
-    TBD: URL to python-dev archives
+    Greg Wilson's questionaire on proposed syntax to some CS grad students
+    http://www.python.org/pipermail/python-dev/2000-July/013139.html
 
 
 Copyright