python3.6 pytest failing with "future feature annotations is not defined"

Running pytests using the python3.6 tox. it started failing with following error.

python3.6 tox failing with following error:

    Error processing line 1 of /home/test/sample/.tox/py36/lib/python3.6/site-packages/_virtualenv.pth:
    
      Traceback (most recent call last):
        File "/usr/lib/python3.6/site.py", line 174, in addpackage
          exec(line)
        File "<string>", line 1, in <module>
        File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/_virtualenv.py", line 3
          from __future__ import annotations
                                           ^
      SyntaxError: future feature annotations is not defined
    
    Remainder of file ignored
    Error processing line 1 of /home/test/sample/.tox/py36/lib/python3.6/site-packages/_virtualenv.pth:
    
      Traceback (most recent call last):
        File "/usr/lib/python3.6/site.py", line 174, in addpackage
          exec(line)
        File "<string>", line 1, in <module>
        File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/_virtualenv.py", line 3
          from __future__ import annotations
                                           ^
      SyntaxError: future feature annotations is not defined
    
    Remainder of file ignored
    Traceback (most recent call last):
      File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
        "__main__", mod_spec)
      File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
        exec(code, run_globals)
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/__main__.py", line 29, in <module>
        from pip._internal.cli.main import main as _main
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/_internal/cli/main.py", line 9, in <module>
        from pip._internal.cli.autocompletion import autocomplete
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/_internal/cli/autocompletion.py", line 10, in <module>
        from pip._internal.cli.main_parser import create_main_parser
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/_internal/cli/main_parser.py", line 9, in <module>
        from pip._internal.build_env import get_runnable_pip
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/_internal/build_env.py", line 19, in <module>
        from pip._internal.cli.spinners import open_spinner
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/_internal/cli/spinners.py", line 9, in <module>
        from pip._internal.utils.logging import get_indentation
      File "/home/test/sample/.tox/py36/lib/python3.6/site-packages/pip/_internal/utils/logging.py", line 8, in <module>
        from dataclasses import dataclass
    ModuleNotFoundError: No module named 'dataclasses'

Both data classes and the future import are Python 3.7 only features. So you either need to use at least Python 3.7 or change your code.

See https://github.com/jugmac00/python-version-cheat-sheet#python-37