[Python-checkins] peps: Integrated many suggestions from c.l.py and others. Nothing

Wed Mar 23 21:24:02 CET 2011

http://hg.python.org/peps/rev/7775a6117a48
changeset: 68:7775a6117a48
user: Barry Warsaw <barry at python.org>
date: Mon Jul 31 15:52:45 2000 +0000
summary:
 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.
files:
 pep-0201.txt | 52 ++++++++++++++++++++++++---------------
 1 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/pep-0201.txt b/pep-0201.txt
--- a/pep-0201.txt
+++ b/pep-0201.txt
@@ -10,14 +10,14 @@
 
 Introduction
 
- This PEP describes the `lockstep iteration' proposal for Python
- 2.0. This PEP tracks the status and ownership of this feature,
- slated for introduction in Python 2.0. It contains a description
- of the feature and outlines changes necessary to support the
- feature. This PEP summarizes discussions held in mailing list
- forums, and provides URLs for further information, where
- appropriate. The CVS revision history of this file contains the
- definitive historical record.
+ This PEP describes the `lockstep iteration' proposal. This PEP
+ tracks the status and ownership of this feature, slated for
+ introduction in Python 2.0. It contains a description of the
+ feature and outlines changes necessary to support the feature.
+ This PEP summarizes discussions held in mailing list forums, and
+ provides URLs for further information, where appropriate. The CVS
+ revision history of this file contains the definitive historical
+ record.
 
 
 Motivation
@@ -25,13 +25,17 @@
 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.
+ loop over more than one sequence in a lock-step fashion. In other
+ 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
- inflexible. This PEP proposes a standard way of performing such
- iterations by introducing a new builtin function called `zip'.
+ The common idioms used to accomplish this are unintuitive. This
+ PEP proposes a standard way of performing such iterations by
+ 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 @@
 [(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
- for-loops. The initial proposals centered around syntactic
- 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).
+ 2.0 beta time frame for syntactic support of lockstep for-loops.
+ Here are two suggestions:
 
+ 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 @@
 [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
-- 
Repository URL: http://hg.python.org/peps
