Add announce of Python 3.5 support dropping

docs/main/changelog.rst

@@ -19,6 +19,7 @@ follows `Semantic versioning`_
 - Add ``Configuration(pydantic_settings=[...])`` argument.
 - Drop support of Python 3.4. There are no immediate breaking changes, but Dependency Injector
   will no longer be tested on Python 3.4 and any bugs will not be fixed.
+- Announce the date of dropping Python 3.5 support (Jan 1st 2022).
 - Fix ``Dependency.is_defined`` attribute to always return boolean value.
 - Fix ``envs_required=False`` behavior in ``Configuration.from_*()`` methods
   to give a priority to the explicitly provided value.

src/dependency_injector/containers.pyx

@@ -6,6 +6,7 @@ import json
 import sys
 import importlib
 import inspect
+import warnings
 
 try:
     import asyncio
@@ -32,6 +33,14 @@ else:
     def unwire(*args, **kwargs):
         raise NotImplementedError('Wiring requires Python 3.6 or above')
 
+if sys.version_info[:2] == (3, 5):
+    warnings.warn(
+        "Dependency Injector will drop support of Python 3.5 after Jan 1st of 2022. "
+        "This does not mean that there will be any immediate breaking changes, "
+        "but tests will no longer be executed on Python 3.5, and bugs will not be addressed.",
+        category=DeprecationWarning,
+    )
+
 
 class WiringConfiguration:
     """Container wiring configuration."""

src/dependency_injector/providers.pyx

@@ -64,6 +64,14 @@ else:  # pragma: no cover
                                     copy.deepcopy(obj.im_self, memo),
                                     obj.im_class)
 
+if sys.version_info[:2] == (3, 5):
+    warnings.warn(
+        "Dependency Injector will drop support of Python 3.5 after Jan 1st of 2022. "
+        "This does not mean that there will be any immediate breaking changes, "
+        "but tests will no longer be executed on Python 3.5, and bugs will not be addressed.",
+        category=DeprecationWarning,
+    )
+
 config_env_marker_pattern = re.compile(
     r'\${(?P<name>[^}^{:]+)(?P<separator>:?)(?P<default>.*?)}',
 )

src/dependency_injector/wiring.py

@@ -6,6 +6,7 @@ import inspect
 import importlib
 import importlib.machinery
 import pkgutil
+import warnings
 import sys
 from types import ModuleType
 from typing import (
@@ -58,6 +59,14 @@ except ImportError:
 from . import providers
 
 
+if sys.version_info[:2] == (3, 5):
+    warnings.warn(
+        "Dependency Injector will drop support of Python 3.5 after Jan 1st of 2022. "
+        "This does not mean that there will be any immediate breaking changes, "
+        "but tests will no longer be executed on Python 3.5, and bugs will not be addressed.",
+        category=DeprecationWarning,
+    )
+
 __all__ = (
     'wire',
     'unwire',