list assignment index out of range error in zip_array class extension method

[trilokacharya]

The class extension method zip_array's action() method has this code:

for _ in queues:
    queues[n] = []

n is set to len(queues) earlier in the method, so this throws index out of range error.

[dbrattli]

Thanks for pointing this out. That code looks ugly.

[trilokacharya]

Thanks for jumping on it so quickly. Any idea when this would get merged into master?

[dbrattli]

I don't have code that triggers the bug, so it's hard for me to know if really fixes the bug. If you could verify the fix, or post some minimal code that triggers the bug, then I can make a unit-test. When we know the fix is correct, then I can merge to master.

[38elements]

Hi, @dbrattli
Hi, @trilokacharya
I tried this by using Python 2.7 and RxPY 1.1.
I reproduced the bug in RxPY 1.1 with the code below and I also confirmed the 72eecb fixes the problem.

from __future__ import print_function
import rx

s = rx.Observable.range(0, 5)
rx.Observable.zip_array(
    s,
    s.skip(1),
    s.skip(2)
).subscribe(print)

result

  File "/usr/local/lib/python2.7/dist-packages/rx/linq/observable/ziparray.py", line 82, in action
    queues[n] = []
IndexError: list assignment index out of range

[dbrattli]

The code in Observable.zip and Observable.zip_arraylooks very similar. What is really the difference between zip_arrayand zip(s1, s2, lambda: x, y: [x, y]) @mattpodwysocki ? I checked the JavaScript sources, and they still have both operators Observable.zipArrayand observableProto.zip that are very similar. Would be nice if we could refactor this code, and implement zip_array (or really zip_list in python) just using zip.

[trilokacharya]

@dbrattli, my understanding from reading the docs at http://reactivex.io/documentation/operators/zip.html is that zip_array is supposed to take a variable number of observables and zip them all.

This is not pretty, but I think it shows the intended behavior:

# Note: please excuse the formatting errors. I can't figure out how to get my formatting to stick in Markup
def flat_add(a,b):
        """ if a = valueA, b = valueB : returns [valueA, valueB]. 
            if a = [V1,V2..Vn], b = valueB : returns [V1,V2..Vn,valueB ]
        """
    if isinstance(a,list):
               a.append(b)
               return a
    else:
               return [a,b]

s1 = rx.Observable.range(0, 5)
s2 = s1.skip(1)
s3 = s1.skip(2)

reduce(lambda a,b:a.zip(b,flat_add),[s1,s2,s3])

"""
result = 
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
""""

[dbrattli]

Yes, but you can do that already with zip:

>>> import rx
>>> def res(*args):
...    return list(args)
...
>>> s1 = rx.Observable.range(0, 5)
>>> s2 = s1.skip(1)
>>> s3 = s1.skip(2)
>>> rx.Observable.zip(s1, s2, s3, res).subscribe(print)
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
<rx.autodetachobserver.AutoDetachObserver object at 0x1025c1320>

Isn't this the same?

[trilokacharya]

You're right. I should've read the description better instead of just looking at the diagram and thinking zip only works on 2 observables at a time.

[dbrattli]

I've now added the simplified Observable.zip_array to the develop branch.

[lock]

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