[Python-checkins] peps: Parallel => Lockstep everywhere. (original) (raw)

georg.brandl python-checkins at python.org
Wed Mar 23 21:23:50 CET 2011

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http://hg.python.org/peps/rev/3c9e17945a3c changeset: 60:3c9e17945a3c user: Barry Warsaw <barry at python.org> date: Fri Jul 28 05:48:25 2000 +0000 summary: Parallel => Lockstep everywhere.

Replaced the reference implementation with one that's closer to what the C code will actually look like; i.e. it obeys the iteration protocol.

Other grammar and spelling fixes.

files: pep-0201.txt | 52 ++++++++++++++++++++------------------- 1 files changed, 27 insertions(+), 25 deletions(-)

diff --git a/pep-0201.txt b/pep-0201.txt --- a/pep-0201.txt +++ b/pep-0201.txt @@ -1,5 +1,5 @@ PEP: 201 -Title: Parallel Iteration +Title: Lockstep Iteration Version: RevisionRevisionRevision Author: bwarsaw at beopen.com (Barry A. Warsaw) Python-Version: 2.0 @@ -10,14 +10,14 @@

Introduction

This PEP describes the `parallel iteration' proposal for Python
2.0, previously known as `parallel for loops'. 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 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.

Motivation @@ -33,9 +33,9 @@ iterations by introducing a new builtin function called `zip'.

-Parallel For-Loops +Lockstep For-Loops

Parallel for-loops are non-nested iterations over two or more

Lockstep for-loops are non-nested iterations over two or more sequences, such that at each pass through the loop, one element from each sequence is taken to compose the target. This behavior can already be accomplished in Python through the use of the map() @@ -70,10 +70,10 @@ [(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 parallel

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 parallel for-loops were

syntax were unresolvable, especially when lockstep for-loops were combined with another proposed feature called `list comprehensions' (see pep-0202.txt).

@@ -140,21 +140,23 @@ Reference Implementation

 Here is a reference implementation, in Python of the zip()

built-in function. These would ultimately be replaced by
equivalent C code.

built-in function. This will be replaced with a C implementation
after final approval.

def zip(*args): if not args: raise TypeError('zip() expects one or more sequence arguments') ret = []

   # find the length of the shortest sequence

```
   shortest = min(*map(len, args))
```
```
   for i in range(shortest):
```
```
       item = []
```
```
       for s in args:
```
```
           item.append(s[i])
```
```
       ret.append(tuple(item))
```
```
   return ret
```

```
   i = 0
```
```
   try:
```
```
       while 1:
```
```
           item = []
```
```
           for s in args:
```
```
               item.append(s[i])
```
```
           ret.append(tuple(item))
```
```
           i = i + 1
```
```
   except IndexError:
```
```
       return ret
```

BDFL Pronouncements @@ -165,8 +167,8 @@ - The function's name. An earlier version of this PEP included an open issue listing 20+ proposed alternative names to zip(). In the face of no overwhelmingly better choice, the BDFL strongly

 prefers zip() due to it's Haskell[2] heritage.  See version 1.7

 of this PEP for the list of alteratives.

 prefers zip() due to its Haskell[2] heritage.  See version 1.7

 of this PEP for the list of alternatives.

zip() shall be a built-in function.

-- Repository URL: http://hg.python.org/peps

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