Use Pickle in favor of PyCall

[yuehhua]

No description provided.

[codecov-commenter]

Codecov Report

Merging #81 (b124a43) into master (6f4aa5a) will increase coverage by 0.94%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
+ Coverage   29.46%   30.41%   +0.94%     
==========================================
  Files          32       33       +1     
  Lines         784      799      +15     
==========================================
+ Hits          231      243      +12     
- Misses        553      556       +3     

Impacted Files	Coverage Δ
src/CiteSeer/CiteSeer.jl	100.00% <ø> (ø)
src/Cora/Cora.jl	100.00% <ø> (ø)
src/MLDatasets.jl	43.75% <ø> (-11.81%)	⬇️
src/PubMed/PubMed.jl	100.00% <ø> (ø)
src/TUDataset/TUDataset.jl	91.07% <ø> (ø)
src/planetoid.jl	98.24% <87.50%> (-1.76%)	⬇️
src/MNIST/utils.jl	76.92% <0.00%> (-13.08%)	⬇️
src/MNIST/Reader/Reader.jl	100.00% <0.00%> (ø)
src/Mutagenesis/Mutagenesis.jl	96.77% <0.00%> (+0.10%)	⬆️
... and 6 more

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[CarloLucibello]

I vaguely remember trying to use Pickle instead of PyCall but failed for some reason, let's hope this works now

[yuehhua]

It seems to work with unit tests, except for failing on deps of Pickle.

[CarloLucibello]

I'm very in favor of dropping PyCall for the leaner Pickle.jl, but passing from julia >= 1.0 support to julia >= 1.6 is a bit too harsh. Can we get Pickle.jl to support at least julia 1.5?
Or even better, maybe we can find some non-pickle data sources for those datasets

[yuehhua]

Fine. I will discuss to @chengchingwen.

[chengchingwen]

It's possible to loose the restriction (at least to 1.5). As far as I can remember, the reason that I drop 1.5 is only because 1.5 and 1.6 use different array summary format and thus break the doctest. It should be fixable.

[yuehhua]

Now, it is loosen to v1.3.

[johnnychen94]

Thank you all for doing this!

[cossio]

Can we tag a release with this? I am having some issues with PyCall which I think would be fixed by this.

[johnnychen94]

Done.

[cossio]

Thanks!