The **attrs** and **cattrs** packages version is incompatible.
Check command:
`pip check --use-feature=2020-resolver`

Code file: https://github.com/apache/airflow/blob/master/setup.py
Commit hash: 9150330
Line number:
694: 'attrs~=19.3'
696: 'cattrs~=1.0'

It will caused the final installed **attrs** version is higher than 20.1.0.

Why this happen?
From the dependency setting of **cattrs**:
https://github.com/Tinche/cattrs/blob/master/setup.py
Commit hash: 2f401b9
Line number:
12: "attrs >= 20.1.0"

setup.py
'cattrs~=1.0',
    'colorlog==4.0.2',
    'connexion[swagger-ui,flask]>=2.6.0,<3',
    'croniter>=0.3.17, <0.4',
    'cryptography>=0.9.3',
    'dill>=0.2.2, <0.4',
    'flask>=1.1.0, <2.0',
    'flask-appbuilder~=3.1.0',
    'flask-caching>=1.3.3, <2.0.0',
    'flask-login>=0.3, <0.5',
    'flask-swagger==0.2.13',
    'flask-wtf>=0.14.2, <0.15',
    'funcsigs>=1.0.0, <2.0.0',
    'graphviz>=0.12',
    'gunicorn>=19.5.0, <20.0',
    'iso8601>=0.1.12',
    'jinja2>=2.10.1, <2.12.0',
    'json-merge-patch==0.2',
    'jsonschema~=3.0',
    'lazy_object_proxy~=1.3',
    'lockfile>=0.12.2',
    'markdown>=2.5.2, <3.0',
    'markupsafe>=1.1.1, <2.0',
    'marshmallow-oneofschema>=2.0.1',
    'pandas>=0.17.1, <2.0',
    'pendulum~=2.0',
    'pep562~=1.0;python_version<"3.7"',
    'psutil>=4.2.0, <6.0.0',
    'pygments>=2.0.1, <3.0',
    'python-daemon>=2.1.1',