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
sha = repo.head.commit.hexsha
        if repo.is_dirty():
            return '.dev0+{sha}.dirty'.format(sha=sha)
        
        return '.release:{version}+{sha}'.format(version=version_, sha=sha)
    else:
        return 'no_git_version'
def write_version(filename: str = os.path.join(*[my_dir, "airflow", "git_version"])):
    """
    Write the Semver version + git hash to file, e.g. ".dev0+2f635dc265e78db6708f59f68e8009abb92c1e65".
    :param str filename: Destination file to write
    """
    text = "{}".format(git_version(version))
    with open(filename, 'w') as file:
        file.write(text)
amazon = [
    'boto3>=1.12.0,<2.0.0',
    'watchtower~=0.7.3',
]
apache_beam = [
    'apache-beam[gcp]',
]
async_packages = [
    'eventlet>= 0.9.7',
    'gevent>=0.13',
    'greenlet>=0.4.9',
]
atlas = [
    'atlasclient>=0.1.2',
]