itertools.izip brokeness

[Bengt Richter]

But you can fix that (only test is what you see ;-) :

Maybe, but not with this version.

from itertools import repeat, chain, izip
it = iter(lambda z=izip(chain([3,5,8],repeat("Bye")), chain([11,22],repeat("Bye"))):z.next(), ("Bye","Bye"))
for t in it: print t

...
(3, 11)
(5, 22)
(8, 'Bye')

(Feel free to generalize ;-)

The problem with this version is that it will stop if for some reason
each iterable contains a 'Bye' at the same place. Now this may seem
far fetched at first. But consider that if data is collected from

ISTM the job of choosing an appropriate sentinel involves making
that not only far fetched but well-nigh impossible ;-)

experiments certain values may be missing. This can be indicated
by a special "Missing Data" value in an iterable. But this "Missing
Data" value would also be the prime canidate for a fill parameter
when an iterable is exhausted.

ISTM that confuses "missing data" with "end of data stream."
I assumed your choice of terminating sentinel ("Bye") would not have
that problem ;-)

Regards,
Bengt Richter

 

[Antoon Pardon]

But you can fix that (only test is what you see ;-) :

Maybe, but not with this version.

from itertools import repeat, chain, izip
it = iter(lambda z=izip(chain([3,5,8],repeat("Bye")), chain([11,22],repeat("Bye"))):z.next(), ("Bye","Bye"))
for t in it: print t
...
(3, 11)
(5, 22)
(8, 'Bye')

(Feel free to generalize ;-)

The problem with this version is that it will stop if for some reason
each iterable contains a 'Bye' at the same place. Now this may seem
far fetched at first. But consider that if data is collected from

ISTM the job of choosing an appropriate sentinel involves making
that not only far fetched but well-nigh impossible ;-)

experiments certain values may be missing. This can be indicated
by a special "Missing Data" value in an iterable. But this "Missing
Data" value would also be the prime canidate for a fill parameter
when an iterable is exhausted.

ISTM that confuses "missing data" with "end of data stream."

"end of data stream" implies "missing data". If I'm doing experiments
with a number of materials under a number of tempertures and I want
to compare how copper, iron and lead behaved then when I compare
the results for 400 K and there is no data for lead, I don't care
whether that is because the measurement for 400K was somehow
lost or unsuable or because they stopped the lead measurements at 350K.

It all boils down to no data for lead at 400K, there is no need that
the processing unit differentiates beteen the different reasons for
the missing data. That difference is only usefull for the loop control.

I assumed your choice of terminating sentinel ("Bye") would not have
that problem ;-)

That is true, but what is adequate in one situation doesn't need to
be adequate in general.