[Python-checkins] CVS: python/nondist/peps pep-0279.txt,1.3,1.4

[Barry Warsaw]

Update of /cvsroot/python/python/nondist/peps
In directory usw-pr-cvs1:/tmp/cvs-serv21255

Modified Files:
	pep-0279.txt 
Log Message:
Raymond Hettinger's latest update, slightly reformatted.


Index: pep-0279.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0279.txt,v
retrieving revision 1.3
retrieving revision 1.4
diff -C2 -d -r1.3 -r1.4
*** pep-0279.txt	4 Feb 2002 21:03:03 -0000	1.3
--- pep-0279.txt	7 Feb 2002 12:08:12 -0000	1.4
***************
*** 61,64 ****
--- 61,69 ----
      generators become final and are not imported from __future__.
  
+     SourceForge contains a working, pure Python simulation of every
+     feature proposed in this PEP [8].  SourceForge also has a separate
+     file with a simulation test suite and working source code for the
+     examples listed used in this PEP [9].
+ 
  
  Specification for new built-ins:
***************
*** 119,123 ****
              yield fun(*args)
  
!     def xzip( *collections ):
          '''
          xzip(...)
--- 124,128 ----
              yield fun(*args)
  
!     def xzip( *collections ):   ### Code from Python Cookbook [6]
          '''
          xzip(...)
***************
*** 147,150 ****
--- 152,161 ----
      not include generators.
  
+     Note B:  An alternate, simplified definition of indexed was proposed:
+ 
+     def indexed( collection, cnt=0, limit=sys.maxint ):
+         'Generates an indexed series:  (0,seqn[0]), (1,seqn[1]) ...'
+         return xzip( xrange(cnt,limit), collection )
+ 
  
  Specification for Generator Comprehensions:
***************
*** 178,181 ****
--- 189,223 ----
      in fact helpful.
  
+     Note B: An iterable instance is returned by the above code.  The
+     purpose is to allow the object to be re-started and looped-over
+     multiple times.  This accurately mimics the behavior of list
+     comprehensions.  As a result, the following code (provided by Oren
+     Tirosh) works equally well with or without 'yield':
+ 
+         letters = [yield chr(i) for i in xrange(ord('a'),ord('z')+1)]
+         digits = [yield str(i) for i in xrange(10)]
+         letdig = [yield l+d for l in letters for d in digits]
+ 
+     Note C: List comprehensions expose their looping variable and
+     leave the variable in the enclosing scope.  The code, [str(i) for
+     i in range(8)] leaves 'i' set to 7 in the scope where the
+     comprehension appears.  This behavior is by design and reflects an
+     intent to duplicate the result of coding a for-loop instead of a
+     list comprehension.  Further, the variable 'i' is in a defined and
+     potentially useful state on the line immediately following the
+     list comprehension.
+ 
+     In contrast, generator comprehensions do not expose the looping
+     variable to the enclosing scope.  The code, [yield str(i) for i in
+     range(8)] leaves 'i' untouched in the scope where the
+     comprehension appears.  This is also by design and reflects an
+     intent to duplicate the result of coding a generator directly
+     instead of a generator comprehension.  Further, the variable 'i'
+     is not in a defined state on the line immediately following the
+     list comprehension.  It does not come into existence until
+     iteration starts.  Since several generators may be running at
+     once, there are potentially multiple, unequal instances of 'i' at
+     any one time.
+ 
  
  Specification for Generator Parameter Passing:
***************
*** 260,271 ****
  
      Loop over the picture files in a directory, shrink them
!     one-at-a-time to thumbnail size using PIL, and send them to a lazy
!     consumer.  That consumer is responsible for creating a large blank
!     image, accepting thumbnails one-at-a-time and placing them in a
!     5x3 grid format onto the blank image.  Whenever the grid is full,
!     it writes-out the large image as an index print.  A FlushStream
!     exception indicates that no more thumbnails are available and that
!     the partial index print should be written out if there are one or
!     more thumbnails on it.
  
  
--- 302,313 ----
  
      Loop over the picture files in a directory, shrink them
!     one-at-a-time to thumbnail size using PIL [7], and send them to a
!     lazy consumer.  That consumer is responsible for creating a large
!     blank image, accepting thumbnails one-at-a-time and placing them
!     in a 5x3 grid format onto the blank image.  Whenever the grid is
!     full, it writes-out the large image as an index print.  A
!     FlushStream exception indicates that no more thumbnails are
!     available and that the partial index print should be written out
!     if there are one or more thumbnails on it.
  
  
***************
*** 349,352 ****
--- 391,407 ----
          http://gnosis.cx/publish/programming/charming_python_b5.txt
  
+     [6] The code fragment for xmap() was found at:
+         http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66448
+ 
+     [7] PIL, the Python Imaging Library can be found at:
+         http://www.pythonware.com/products/pil/
+ 
+     [8] A pure Python simulation of every feature in this PEP is at:
+         http://sourceforge.net/tracker/download.php?group_id=5470&atid=305470&file_id=17348&aid=513752
+ 
+     [9] The full, working source code for each of the examples in this PEP
+         along with other examples and tests is at:
+         http://sourceforge.net/tracker/download.php?group_id=5470&atid=305470&file_id=17412&aid=513756
+ 
  
  Copyright
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*** 361,364 ****
  fill-column: 70
  End:
- 
- 
--- 416,417 ----