chore: Add deprecation notice for 3.7. (#1371)

Author: clundin25

README.rst

@@ -37,6 +37,16 @@ Supported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 Python >= 3.7
 
+**NOTE**:
+Python 3.7 was marked as `unsupported`_ by the python community in June 2023.
+We recommend that all developers upgrade to Python 3.8 and newer as soon as
+they can. Support for Python 3.7 will be removed from this library after
+January 1 2024. Previous releases that support Python 3.7 will continue to be available
+for download, but releases after January 1 2024 will only target Python 3.8 and
+newer.
+
+.. _unsupported: https://devguide.python.org/versions/#unsupported-versions
+
 Unsupported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Python == 2.7:  The last version of this library with support for Python 2.7

google/auth/__init__.py

@@ -15,6 +15,8 @@
 """Google Auth Library for Python."""
 
 import logging
+import sys
+import warnings
 
 from google.auth import version as google_auth_version
 from google.auth._default import (
@@ -29,5 +31,28 @@
 
 __all__ = ["default", "load_credentials_from_file", "load_credentials_from_dict"]
 
+
+class Python37DeprecationWarning(DeprecationWarning):  # pragma: NO COVER
+    """
+    Deprecation warning raised when Python 3.7 runtime is detected.
+    Python 3.7 support will be dropped after January 1, 2024. See
+    https://cloud.google.com/python/docs/python37-sunset/ for more information.
+    """
+
+    pass
+
+
+# Checks if the current runtime is Python 3.7.
+if sys.version_info.major == 3 and sys.version_info.minor == 7:  # pragma: NO COVER
+    message = (
+        "After January 1, 2024, new releases of this library will drop support "
+        "for Python 3.7. More details about Python 3.7 support "
+        "can be found at https://cloud.google.com/python/docs/python37-sunset/"
+    )
+
+    # Configure the Python37DeprecationWarning warning so that it is only emitted once.
+    warnings.simplefilter("once", Python37DeprecationWarning)
+    warnings.warn(message, Python37DeprecationWarning)
+
 # Set default logging handler to avoid "No handler found" warnings.
 logging.getLogger(__name__).addHandler(logging.NullHandler())

google/oauth2/__init__.py

@@ -13,3 +13,28 @@
 # limitations under the License.
 
 """Google OAuth 2.0 Library for Python."""
+
+import sys
+import warnings
+
+
+class Python37DeprecationWarning(DeprecationWarning):  # pragma: NO COVER
+    """
+    Deprecation warning raised when Python 3.7 runtime is detected.
+    Python 3.7 support will be dropped after January 1, 2024. See
+    https://cloud.google.com/python/docs/python37-sunset/ for more information.
+    """
+
+    pass
+
+
+# Checks if the current runtime is Python 3.7.
+if sys.version_info.major == 3 and sys.version_info.minor == 7:  # pragma: NO COVER
+    message = (
+        "After January 1, 2024, new releases of this library will drop support "
+        "for Python 3.7. More details about Python 3.7 support "
+        "can be found at https://cloud.google.com/python/docs/python37-sunset/"
+    )
+    # Configure the Python37DeprecationWarning warning so that it is only emitted once.
+    warnings.simplefilter("once", Python37DeprecationWarning)
+    warnings.warn(message, Python37DeprecationWarning)