[Python] Bump attrs, cattrs versions for Python 3.7+

[setu4993]

Ran into a weird edge case today where import for looker_sdk failed because of a version issue with attrs, which was on 19.3.0 but cattrs required attr>=20.1.0 (this line requires attrs > 20.1.0). Tracelog below, but running a pip install -U attrs fixed the issue. Bumping it up in here, along with the version (feel free to update the version appropriately if that's an error on my end).

Tracelog:

...
/opt/conda/lib/python3.7/site-packages/looker_sdk/__init__.py in <module>
     25 from looker_sdk.rtl import api_settings
     26 from looker_sdk.rtl import requests_transport
---> 27 from looker_sdk.rtl import serialize
     28 from looker_sdk.rtl import auth_session
     29 

/opt/conda/lib/python3.7/site-packages/looker_sdk/rtl/serialize.py in <module>
     37 )
     38 
---> 39 import cattr
     40 
     41 from looker_sdk.rtl import model

/opt/conda/lib/python3.7/site-packages/cattr/__init__.py in <module>
----> 1 from .converters import Converter, GenConverter, UnstructureStrategy
      2 from .gen import override
      3 
      4 __all__ = (
      5     "global_converter",

/opt/conda/lib/python3.7/site-packages/cattr/converters.py in <module>
     14 )
     15 
---> 16 from attr import fields, resolve_types
     17 
     18 from ._compat import (

ImportError: cannot import name 'resolve_types' from 'attr' (/opt/conda/lib/python3.7/site-packages/attr/__init__.py)

[joeldodge79]

thanks for finding this. We need to maintain support for python 3.6 and it looks like that was dropped in cattrs 1.1.0 so we'll need to either pin cattrs == 1.0.0 or find a fancy way of switching based on python version (similar to how python-dateutil and typing-extensions are added)

[joeldodge79]

If you have cycles to figure out allowing higher cattrs versions conditional on python version that would be much appreciated! Otherwise for now let's just pin it to 1.0.0 so new installations aren't broken

[setu4993]

Thanks Joel! I can get this in place later today.

[setu4993]

@joeldodge79 : Done. Tested installing on my brand new venvs on 36 and 37, and the right versions get installed on both.

[joeldodge79]

Awesome, thank you! I'll get this published shortly

[setu4993]

Thanks Joel!

[joeldodge79]

https://pypi.org/project/looker-sdk/0.1.3b20/ is up