`typing.Protocol` is not supported in Python < 3.8

[skylander86]

Bug report

What's wrong

On Python 3.7, importing django_stubs_ext causes ImportError: cannot import name 'Protocol' from 'typing' (/usr/local/lib/python3.7/typing.py).

This issue only surfaced in django-stubs 1.10.0 and django-stubs-ext 0.4.0.

The workaround in the meantime is to stay on 1.9.0 and 0.3.0.

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/commands/check.py", line 69, in handle
    databases=options['databases'],
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 423, in check
    databases=databases,
  File "/usr/local/lib/python3.7/site-packages/django/core/checks/registry.py", line 76, in run_checks
    new_errors = check(app_configs=app_configs, databases=databases)
  File "/usr/local/lib/python3.7/site-packages/django/core/checks/templates.py", line 29, in check_string_if_invalid_is_string
    for conf in settings.TEMPLATES:
  File "/usr/local/lib/python3.7/site-packages/django/conf/__init__.py", line 82, in __getattr__
    self._setup(name)
  File "/usr/local/lib/python3.7/site-packages/django/conf/__init__.py", line 69, in _setup
    self._wrapped = Settings(settings_module)
  File "/usr/local/lib/python3.7/site-packages/django/conf/__init__.py", line 170, in __init__
    mod = importlib.import_module(self.SETTINGS_MODULE)
  File "/usr/local/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/testsite/testsite/settings.py", line 4, in <module>
    import django_stubs_ext
  File "/usr/local/lib/python3.7/site-packages/django_stubs_ext/__init__.py", line 5, in <module>
    from .types import AnyAttrAllowed as AnyAttrAllowed
  File "/usr/local/lib/python3.7/site-packages/django_stubs_ext/types.py", line 1, in <module>
    from typing import Any, Protocol
ImportError: cannot import name 'Protocol' from 'typing' (/usr/local/lib/python3.7/typing.py)

How is that should be

If Python 3.7 compatibility is desired, we shuld use Protocol from typing_extensions instead.

System information

• OS:
• python version: 3.7
• django version: 3.2
• mypy version: 0.910
• django-stubs version: 1.10.0
• django-stubs-ext version: 0.4.0

[sobolevn]

Please, send a PR!