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
"mongo": mongo,
    "mysql": mysql,
    "odbc": odbc,
    "openfaas": [],
    "opsgenie": [],
    "oracle": oracle,
    "pagerduty": pagerduty,
    "papermill": papermill,
    "plexus": plexus,
    "postgres": postgres,
    "presto": presto,
    "qubole": qds,
    "redis": redis,
    "salesforce": salesforce,
    "samba": samba,
    "segment": segment,
    "sftp": ssh,
    "singularity": singularity,
    "slack": slack,
    "snowflake": snowflake,
    "sqlite": [],
    "ssh": ssh,
    "vertica": vertica,
    "yandex": yandexcloud,
    "zendesk": zendesk,
}
EXTRAS_REQUIREMENTS: Dict[str, Iterable[str]] = {
    'all_dbs': all_dbs,
    'amazon': amazon,
    'apache.atlas': atlas,