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No one likes the name inreverse().

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Raymond Hettinger 2003-10-28 22:39:22 +00:00
parent e680cb67de
commit f7f0a4d4ea
1 changed files with 13 additions and 10 deletions
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pep-0322.txt
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@ -46,27 +46,27 @@ does arise regularly in practice. See `Real World Use Cases`_ below.
Proposal Proposal
======== ========
Add a builtin function called *inreverse()* that makes a reverse Add a builtin function called *ireverse()* that makes a reverse
iterator over sequence objects that support __getitem__() and iterator over sequence objects that support __getitem__() and
__len__(). __len__().
The above examples then simplify to:: The above examples then simplify to::
for i in inreverse(xrange(n)): for i in ireverse(xrange(n)):
print seqn[i] print seqn[i]
:: ::
for elem in inreverse(seqn): for elem in ireverse(seqn):
print elem print elem
The core idea is that the clearest, least error-prone way of specifying The core idea is that the clearest, least error-prone way of specifying
reverse iteration is to specify it in a forward direction and then say reverse iteration is to specify it in a forward direction and then say
*inreverse*. *ireverse*.
The implementation could be as simple as:: The implementation could be as simple as::
def inreverse(x): def ireverse(x):
i = len(x) i = len(x)
while i > 0: while i > 0:
i -= 1 i -= 1
@ -83,13 +83,16 @@ Alternative Method Names
======================== ========================
* *backwards* -- more pithy, less explicit * *backwards* -- more pithy, less explicit
* *ireverse* -- reminiscent of imap(), izip(), and ifilter() * *inreverse* -- no one seems to like this one except me
The name *reverse* is not a candidate because it duplicates the name
of the list.reverse() which mutates the underlying list.
Custom Reverse Custom Reverse
============== ==============
Objects may optionally provide an *__inreverse__* method that returns Objects may optionally provide an *__ireverse__* method that returns
a custom reverse iterator. a custom reverse iterator.
This allows reverse() to be applied to objects that do not have This allows reverse() to be applied to objects that do not have
@ -140,7 +143,7 @@ library and comments on why reverse iteration was necessary:
elements from an ever diminishing pool. In fact, the algorithm can elements from an ever diminishing pool. In fact, the algorithm can
be run in a forward direction but is less intuitive and rarely be run in a forward direction but is less intuitive and rarely
presented that way in literature. The replacement code presented that way in literature. The replacement code
``for i in inreverse(xrange(1, len(x)))`` is much easier ``for i in ireverse(xrange(1, len(x)))`` is much easier
to verify visually. to verify visually.
* rfc822.Message.__delitem__() uses:: * rfc822.Message.__delitem__() uses::
@ -158,7 +161,7 @@ Active Alternative
A simpler, but limited alternative is to create a builtin that takes A simpler, but limited alternative is to create a builtin that takes
the same arguments as range() but returns a reverse iterator over the the same arguments as range() but returns a reverse iterator over the
range. The idea is that much of the benefit of inreverse() comes range. The idea is that much of the benefit of ireverse() comes
reducing the intellectual effort it takes to express the arguments for reducing the intellectual effort it takes to express the arguments for
[x]range() when going backwards. A good name is needed for this [x]range() when going backwards. A good name is needed for this
alternative -- revrange() is cleanest so far. alternative -- revrange() is cleanest so far.
@ -167,7 +170,7 @@ alternative -- revrange() is cleanest so far.
Rejected Alternative Rejected Alternative
==================== ====================
Several variants were submitted that attempted to apply inreverse() Several variants were submitted that attempted to apply ireverse()
to all iterables by running the iterable to completion, saving the to all iterables by running the iterable to completion, saving the
results, and then returning a reverse iterator over the results. results, and then returning a reverse iterator over the results.
While satisfying some notions of full generality, running the input While satisfying some notions of full generality, running the input