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
"""
    Checks if package should be excluded.
    :param package: package name (beginning of it)
    :param exclusion_list: list of excluded packages
    :return: true if package should be excluded
    """
    return any(package.startswith(excluded_package) for excluded_package in exclusion_list)
devel_all = [package for package in devel_all if not is_package_excluded(
    package=package,
    exclusion_list=PACKAGES_EXCLUDED_FOR_ALL)
]
devel_ci = [package for package in devel_all if not is_package_excluded(
    package=package,
    exclusion_list=PACKAGES_EXCLUDED_FOR_CI + PACKAGES_EXCLUDED_FOR_ALL)
]
EXTRAS_REQUIREMENTS.update(
    {
        'all': devel_all,
        'devel_ci': devel_ci,
    }
)
INSTALL_REQUIREMENTS = [
    'alembic>=1.2, <2.0',
    'argcomplete~=1.10',
    'attrs~=19.3',
    'cached_property~=1.5',