BigQuery: 'pyarrow' support cannot be used with Python 3.7

[crwilcox]

Pandas/Cython doesn't currently support 3.7. Once it does we need to enable 3.7 testing on BigQuery.

Collecting pandas>=0.17.1 (from google-cloud-monitoring==0.29.0)
Using cached https://files.pythonhosted.org/packages/08/01/803834bc8a4e708aedebb133095a88a4dad9f45bbaf5ad777d2bea543c7e/pandas-0.22.0.tar.gz
Could not find a version that satisfies the requirement Cython (from versions: )
No matching distribution found for Cython

[theacodes]

Is there an upstream issue for Cython and Pandas to provide 3.7 wheels?

[crwilcox]

I came across a bunch of closed issues for Cython (which works for 3.7 but doesn't seem to ship a wheel at this time). I couldn't find much at all regarding Pandas.

[tswast]

I think we need to keep open to drop removal of Pandas from 3.7 tests once Pandas adds a package for 3.7.

Upstream issues:

• Cython: per Cython incompatible with Python 3.7 cython/cython#1978 it should work with HEAD, but possibly not packaged to support 3.7 on PyPI
• Numpy: PyPi package not compatible with CPython nightly (3.7) numpy/numpy#10500
• Pandas: TST/COMPAT: test Python 3.7 pandas-dev/pandas#20552

[tseaver]

Pandas 0.23.3 claims (working) support for Python 3.7.

The release page also notes Pandas will be dropping Python 2.7 support for new feature releases as of 2019-01-01.

[tseaver]

However, pyarrow does not yet support Python 3.7 in its latest release.

[tseaver]

The forthcoming Pyarrow 0.11.0 release is supposed to have wheels for Python 3.7.

[tswast]

Fixed by #7610.

Removing outdated comment in #8785.