Add zstd compression read support for uproot

[oshadura]

Locally I have green tests:
Ran 106 tests in 33.114s
OK

[jpivarski]

Wow, this looks perfect! Highly approved! (Oh, two mistakes; but after that, highly approved.)

• Python zstd library is an optional dependency.
• Oh, I found an error: the installation instructions for conda should be changed. (See compressed.py:89 inline comment.)
• It's in the tests-require and manually loaded in Travis (like the others).
• Test samples with the new compression algorithm (HZZ and Zmumu).
• Unit tests use the new test samples, comparing detailed TTree values (test_compression.py, content1 and content2.
• sample4version.C is ready to make new ROOT files with zstd, but that will wait until ROOT 6.20 comes out.
• Help strings have been updated.
• New constants in const.py.

The failure of the AppVeyor tests is due to appveyor.yml:53 (see inline comment).

[oshadura]

@jpivarski I will add zstd for writing as soon we will have release.

[jpivarski]

@oshadura Writing with zstd should probably be a new pull request, and it may be after the 3.11.0 release.

When you do add writing with zstd, be sure to ping @reikdas so he can verify that nothing was missed.

[jpivarski]

@oshadura I pushed a correction to your branch, but it hasn't shown up here yet (for me): https://github.com/oshadura/uproot/commits/add-zstd-compression-support

When it does (and tests pass), I'll merge this unless you tell me not to.

[jpivarski]

@oshadura Could you try pulling in your branch, verifying that my changes to uproot/source/compressed.py are there (where I dropped the -c XYZ option in the install messages), and maybe make some trivial change to push it here? I don't know why it isn't showing up.

[chrisburr]

I was looking at adding the conda-forge package and I noticed there are two different sets of Python bindings. Both are linked from facebook's webpage:

• https://pypi.org/project/zstd/: Currently used
• https://pypi.org/project/zstandard/: More downloads/GitHub activity and already on conda-forge

Is there a reason for preferring zstd?

[oshadura]

@jpivarski

I was looking at adding the conda-forge package and I noticed there are two different sets of Python bindings. Both are linked from facebook's webpage:

* https://pypi.org/project/zstd/: Currently used

* https://pypi.org/project/zstandard/: More downloads/GitHub activity and already on conda-forge

Is there a reason for preferring zstd?

Thanks, let me check!

[oshadura]

https://pypi.org/project/zstd/

@jpivarski @chrisburr thanks for checking, zstandard package is definitely better! (it supports much more functionality, such as dictionary generation and streaming API). I updated PR accordingly.

[jpivarski]

Okay, great! When the tests pass, should I merge this, @oshadura?

[oshadura]

Okay, great! When the tests pass, should I merge this, @oshadura?

Yes, please!

[jpivarski]

After this last force-push?

oshadura force-pushed the oshadura:add-zstd-compression-support branch from 1d8af06 to 83169d9 2 minutes ago

[oshadura]

@jpivarski yeap, now I am ready I think.