xarray 0.12.0 Fails To Import On Python 3.5.2

[ancantus]

Error Code Example

Problem was discovered when xarray was pulled in via a pip dependency.

import xarray

Problem description

xarray seems to now use typing.ClassVar which is unavailable in python 3.5.2

Output of import xarray

Traceback (most recent call last): File "", line 1, in File "$VENV_PATH/lib/python3.5/site-packages/xarray/__init__.py", line 26, in from .coding.cftime_offsets import cftime_range File "$VENV_PATH/lib/python3.5/site-packages/xarray/coding/cftime_offsets.py", line 46, in from typing import ClassVar, Optional ImportError: cannot import name 'ClassVar'

Suggested Solution

• Remove typing.ClassVar from xarray
• Updated setup.py for 0.12.0 to reflect new python version requirement for the package.

[max-sixty]

Thanks @ancantus! Sorry for that.

Python 3.5.3 does support ClassVar, which is how it passed our tests. That was released 2017-01-17. So this shouldn't be too common.

We should have specified in setup.py. I'll do a PR now.

@shoyer do you think we need to do anything immediately re PyPI?

[shoyer]

Thanks for the report. We should fix xarray on Python 3.5.0.

Probably the simplest thing to do would be to guard the import in a typing.TYPE_CHECKING block and replace ClassVar[something] in the code with 'ClassVar[something]'. So you'll need at least Python 3.5.3 to do type checking of xarray, but it won't be required for users.

[max-sixty]

Great, made that change. (my search didn't turn up any references to ClassVar outside the comments, so only did the guard)

[ancantus]

Thanks! Came up for me cause the Ubuntu LTS Xenial uses Python 3.5.2 as its default installed version.

[dcherian]

Closed by #2831