[Python-checkins] CVS: python/nondist/peps pep-0201.txt,1.2,1.3

2000年7月18日 21:19:57 -0700

Update of /cvsroot/python/python/nondist/peps
In directory slayer.i.sourceforge.net:/tmp/cvs-serv10215
Modified Files:
	pep-0201.txt 
Log Message:
In the examples section, show how zip() is reversible.
Patches to the reference implementation:
 __getitem__() raises IndexError immediately if no sequences were
 given.
 __len__() returns 0 if no sequences were given.
 __cmp__() new method
Added a little more explanation to raise-a-TypeError-for-zip(a)
Added `fold' as one of the alternative names proposed.
Index: pep-0201.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0201.txt,v
retrieving revision 1.2
retrieving revision 1.3
diff -C2 -r1.2 -r1.3
*** pep-0201.txt	2000年07月17日 18:49:21	1.2
--- pep-0201.txt	2000年07月19日 04:19:54	1.3
***************
*** 173,177 ****
--- 173,197 ----
 [(1, 5, 9, 12), (2, 6, 10, 13), (3, 7, 11, None), (4, 8, None, None)]

+ Note that when the sequences are of the same length, zip() is
+ reversible:

+ >>> a = (1, 2, 3)
+ >>> b = (4, 5, 6)
+ >>> x = zip(a, b)
+ >>> y = zip(*x) # alternatively, apply(zip, x)
+ >>> z = zip(*y) # alternatively, apply(zip, y)
+ >>> x
+ [(1, 4), (2, 5), (3, 6)]
+ >>> y
+ [(1, 2, 3), (4, 5, 6)]
+ >>> z
+ [(1, 4), (2, 5), (3, 6)]
+ >>> x == z
+ 1
+ 
+ It is not possible to reverse zip this way when the sequences are
+ not all the same length.
+ 
+ 

 Reference Implementation
***************
*** 196,199 ****
--- 216,221 ----

 def __getitem__(self, i):
+ if not self.__sequences:
+ raise IndexError
 ret = []
 exhausted = 0
***************
*** 219,222 ****
--- 241,246 ----
 if shortest < 0 or slen < shortest:
 shortest = slen
+ if shortest < 0:
+ return 0
 return shortest
 longest = 0
***************
*** 227,230 ****
--- 251,278 ----
 return longest

+ def __cmp__(self, other):
+ i = 0
+ smore = 1
+ omore = 1
+ while 1:
+ try:
+ si = self[i]
+ except IndexError:
+ smore = 0
+ try:
+ oi = other[i]
+ except IndexError:
+ omore = 0
+ if not smore and not omore:
+ return 0
+ elif not smore:
+ return -1
+ elif not omore:
+ return 1
+ test = cmp(si, oi)
+ if test:
+ return test
+ i = i + 1
+ 
 def __str__(self):
 ret = []
***************
*** 336,340 ****
 3) Raises TypeError

! Pros: None

 Cons: needless restriction
--- 384,389 ----
 3) Raises TypeError

! Pros: zip(a) doesn't make much sense and could be confusing
! to explain.

 Cons: needless restriction
***************
*** 346,352 ****
 (but are not limited to!): marry, weave, parallel, lace, braid,
 interlace, permute, furl, tuples, lists, stitch, collate, knit,
! plait, and with. All have disadvantages, and there is no clear
! unanimous choice, therefore the decision was made to go with
! `zip' because the same functionality is available in other
 languages (e.g. Haskell) under the name `zip'[2].

--- 395,401 ----
 (but are not limited to!): marry, weave, parallel, lace, braid,
 interlace, permute, furl, tuples, lists, stitch, collate, knit,
! plait, fold, and with. All have disadvantages, and there is no
! clear unanimous choice, therefore the decision was made to go
! with `zip' because the same functionality is available in other
 languages (e.g. Haskell) under the name `zip'[2].