En Fri, 17 Jul 2009 21:31:44 -0300, Zac Burns <zac...@gmail.com> escribió:
I would like a set like object that when iterated maintains a count of
where iteration stopped and then re-orders itself based on that count
so that the iteration stopped on the most bubble to the top.
An example use case for this would be for something like a large table
of regular expressions that would be iterated over trying to match in
some string. If some regular expressions are more statistically more
successful then the iteration will generally be short.
If you require a certain order, it's not a set; better to use a list.
The code below extends the builtin list type to add a "promote" method;
lst.promote(3) "bubbles" lst[3] up (exchanging lst[3] with lst[2]). It's
thread safe, and O(1).
<code>
import threading
class XList(list):
#
@property
def lock(self):
lock = getattr(self, '_lock', None)
if lock is None: lock = self._lock = threading.Lock()
return lock
#
def promote(self, index):
if index<0: index += len(self)
if index>0:
with self.lock:
self[index], self[index-1] = self[index-1], self[index]
</code>
py> a = XList('python')
py> a
['p', 'y', 't', 'h', 'o', 'n']
py> a.promote(3)
py> a
['p', 'y', 'h', 't', 'o', 'n']
py> a.promote(2)
py> a
['p', 'h', 'y', 't', 'o', 'n']
py> a.promote(-1)
py> a
['p', 'h', 'y', 't', 'n', 'o']
py> a.promote(0)
py> a
['p', 'h', 'y', 't', 'n', 'o']
An example, looking for a matching regular expression:
for index,expr in enumerate(exprlist):
m = expr.match(txt)
if m:
dosomethingwith(m)
exprlist.promote(index)
break
After many calls, the most frequently matched expressions appear towards
the front of the list.
Extend to also include a mapping version
I'm unsure if this point is still applicable. I'm using a list here, not a
set as in your original proposal.
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
