Implementation of isplit, a function that splits iterators into two equal ones, which return similar values, but are exact copies of one another.
Python, 87 lines
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class _IDup(object):
"""Internal class used only to keep a reference on the actual iterator,
and to do housekeeping."""
def __init__(self,iterin):
self.__iter = iterin
self.__iterno = 0
self.__iteritems = []
self.__hasstopped = None
def registerIter(self,oldno=-1):
iterno = self.__iterno
self.__iterno += 1
if oldno == -1:
self.__iteritems.append([])
else:
self.__iteritems.append(
copy.deepcopy(self.__iteritems[oldno])
)
return iterno
def getNext(self,iterno):
if self.__iteritems[iterno]:
iteritem = self.__iteritems[iterno].pop(0)
elif self.__hasstopped is not None:
raise self.__hasstopped
else:
try:
iteritem = self.__iter.next()
except StopIteration, e:
self.__hasstopped = e
raise
for id, i in enumerate(self.__iteritems):
if id <> iterno:
i.append(copy.deepcopy(iteritem))
return iteritem
class _IDupped(object):
"""Duplicated Iterator class. Each iterator you get by calling isplit
or split on a splitted iterator will be of this type."""
def __init__(self,idup,oldno=-1):
self.__idup = idup
self.__iterno = idup.registerIter(oldno)
def next(self):
return self.__idup.getNext(self.__iterno)
def split(self):
"""Split this iterator into two pieces. The original iterator
is still callable, as is the sub-iterator."""
return _IDupped(self.__idup,self.__iterno)
def __iter__(self):
return self
def isplit(iterin,splitno=2):
idup = _IDup(iterin)
iduppeds = []
for i in range(splitno):
iduppeds.append(_IDupped(idup))
return tuple(iduppeds)
# Create first few iterators.
test = ["hello","how","are","you?"]
x, y = isplit(iter(test))
# Test print of iterator y.
print "First item of y."
print y.next()
# Create new iterator z after first element of y.
z = y.split()
# Print rest of the elements.
print "Rest in x."
for i in x:
print i
print "Rest in y."
for i in y:
print i
print "Rest in z."
for i in z:
print i
|
The problem of having to split iterators occured to me when I had one iterator, which kept returning lines from a source-file, which I wanted two different functions to process simultaneously. These functions ran in the same context, but I thought it was cleaner passing each function its own iterator versus calling both functions from a loop which read the lines one by one from the file.
Tags: algorithms
Here's a simpler and faster implementation.
Version that can return more than two iterators.