Addressing Issue 158: Unexpected Sequence Wrapping from Grouped

[stephan-rayner]

Elements That are Lists in a Sequence Will Remain Lists When Grouped.

Much of the details around this PR can be found in issue 158. I added a quick summary below to get everyone on the same page.

from functional import seq
s = [[i,i+1] for i in range(10)]
for batch in seq(s).grouped(3):
    for item in batch:
        print(f'{item} -- {type(item)}')

Running the above code sample and printing the output (were it captured) will result in the following output.

[0, 1] -- <class 'functional.pipeline.Sequence'>
[1, 2] -- <class 'list'>
[2, 3] -- <class 'list'>
[3, 4] -- <class 'functional.pipeline.Sequence'>
[4, 5] -- <class 'list'>
[5, 6] -- <class 'list'>
[6, 7] -- <class 'functional.pipeline.Sequence'>
[7, 8] -- <class 'list'>
[8, 9] -- <class 'list'>
[9, 10] -- <class 'functional.pipeline.Sequence'>

The same check run with these changes produces the output below.

[0, 1] -- <class 'list'>
[1, 2] -- <class 'list'>
[2, 3] -- <class 'list'>
[3, 4] -- <class 'list'>
[4, 5] -- <class 'list'>
[5, 6] -- <class 'list'>
[6, 7] -- <class 'list'>
[7, 8] -- <class 'list'>
[8, 9] -- <class 'list'>
[9, 10] -- <class 'list'>

Special thanks to @evanw2 for his leg work on this issue. The discovery in the first place and all of the investigation made this a lot easier #ShouldersOfGiants.

[codecov]

Codecov Report

Merging #160 (e81d110) into master (6c50426) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #160   +/-   ##
=======================================
  Coverage   97.97%   97.98%           
=======================================
  Files          12       12           
  Lines        2226     2237   +11     
=======================================
+ Hits         2181     2192   +11     
  Misses         45       45           

Impacted Files	Coverage Δ
functional/pipeline.py	98.08% <100.00%> (ø)
functional/test/test_functional.py	98.93% <100.00%> (+0.01%)	⬆️
functional/transformations.py	100.00% <100.00%> (ø)

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[evanw2]

Thanks for making this! Looks good to me.

[EntilZha]

LGTM as well, thanks for the fix!