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
]
qds = [
    'qds-sdk>=1.10.4',
]
rabbitmq = [
    'amqp',
]
redis = [
    'redis~=3.2',
]
salesforce = [
    'simple-salesforce>=1.0.0',
]
samba = [
    'pysmbclient>=0.1.3',
]
segment = [
    'analytics-python>=1.2.9',
]
sendgrid = [
    'sendgrid>=6.0.0,<7',
]
sentry = [
    'blinker>=1.1',
    'sentry-sdk>=0.8.0',
]
singularity = ['spython>=0.0.56']
slack = [
    'slackclient>=2.0.0,<3.0.0',
]