On Thu, 05 Jan 2006 07:42:25 GMT, [EMAIL PROTECTED] (Bengt Richter) wrote:
>On 4 Jan 2006 15:20:43 -0800, "Raymond Hettinger" <[EMAIL PROTECTED]> wrote:
>
[ ... 5 options enumerated ... ]
>>
>>
>6. Could modify izip so that one could write
>
> from itertools import izip
> zipit = izip(*seqs) # bind iterator object to preserve access to
> its state later
> for tup in zipit:
> # do something with tup as now produced
> for tup in zipit.rest(sentinel):
> # tup starts with the tuple that would have been returned if all
> sequences
> # had been sampled and sentinel substituted where StopIteration
> happened.
> # continuing until but not including (sentinel,)*len(seqs)
>
>This would seem backwards compatible, and also potentially allow you to use
>the rest mode
>from the start, as in
>
> for tup in izip(*seqs).rest(sentinel):
> # process tup and notice sentinel for yourself
>
Demo-of-concept hack: only tested as you see below
----< izip2.py >-----------------------------------------------------
class izip2(object):
"""
works like itertools.izip except that
if a reference (e.g. it) to the stopped iterator is preserved,
it.rest(sentinel) returns an iterator that will continue
to return tuples with sentinel substituted for items from
exhausted sequences, until all sequences are exhausted.
"""
FIRST, FIRST_STOP, FIRST_REST, REST, REST_STOP = xrange(5)
def __init__(self, *seqs):
self.iters = map(iter, seqs)
self.restmode = self.FIRST
def __iter__(self): return self
def next(self):
if not self.iters: raise StopIteration
if self.restmode == self.FIRST:
tup=[]
try:
for i, it in enumerate(self.iters):
tup.append(it.next())
return tuple(tup)
except StopIteration:
self.restmode = self.FIRST_STOP # stopped, not rest-restarted
self.tup=tup;self.i=i
raise
elif self.restmode==self.FIRST_STOP: # normal part exhausted
raise StopIteration
elif self.restmode in (self.FIRST_REST, self.REST):
if self.restmode == self.FIRST_REST:
tup = self.tup # saved
self.restmode = self.REST
else:
tup=[]
for it in self.iters:
try: tup.append(it.next())
except StopIteration: tup.append(self.sentinel)
tup = tuple(tup)
if tup==(self.sentinel,)*len(self.iters):
self.restmode = self.REST_STOP
raise StopIteration
return tuple(tup)
elif self.restmode==self.REST_STOP: # rest part exhausted
raise StopIteration
else:
raise RuntimeError('Bad restmode: %r'%self.restmode)
def rest(self, sentinel=''):
self.sentinel = sentinel
if self.restmode==self.FIRST: # prior to any sequence end
self.restmode = self.REST
return self
self.tup.append(sentinel)
for it in self.iters[self.i+1:]:
try: self.tup.append(it.next())
except StopIteration: self.tup.append(sentinel)
self.restmode = self.FIRST_REST
return self
def test():
assert list(izip2())==[]
assert list(izip2().rest(''))==[]
it = izip2('ab', '1')
assert list(it)==[('a', '1')]
assert list(it.rest())==[('b', '')]
it = izip2('a', '12')
assert list(it)==[('a', '1')]
assert list(it.rest())==[('', '2')]
it = izip2('ab', '12')
assert list(it)==[('a', '1'), ('b', '2')]
assert list(it.rest())==[]
it = izip2(xrange(3), (11,22), 'abcd')
assert list(it) == [(0, 11, 'a'), (1, 22, 'b')]
assert list(it.rest(None)) == [(2, None, 'c'), (None, None, 'd')]
print 'test passed'
if __name__ == '__main__': test()
---------------------------------------------------------------------
Using this, Antoon's example becomes:
>>> from izip2 import izip2
>>> it = izip2([3,5,8], [11,22])
>>> for t in it: print t
...
(3, 11)
(5, 22)
>>> for t in it.rest('Bye'): print t
...
(8, 'Bye')
Want to make an efficient C version, Raymond? ;-)
Regards,
Bengt Richter
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