feat(identifiers): Check Python Runtime

Issues a WARNING if the Python Version will become unsupported.
Prints an ERROR to STDERR if Python Version is unsupported.
Will start issuing WARNING for Python Version less than 3.6.
Will start printing ERROR for Python Version less than 3.5 AFTER Jan 1st, 2022.

src/aws_encryption_sdk/__init__.py

@@ -12,15 +12,14 @@
 # language governing permissions and limitations under the License.
 """High level AWS Encryption SDK client functions."""
 # Below are imported for ease of use by implementors
-
 import warnings
 
 import attr
 
 from aws_encryption_sdk.caches.local import LocalCryptoMaterialsCache  # noqa
 from aws_encryption_sdk.caches.null import NullCryptoMaterialsCache  # noqa
 from aws_encryption_sdk.exceptions import AWSEncryptionSDKClientError  # noqa
-from aws_encryption_sdk.identifiers import Algorithm, CommitmentPolicy, __version__  # noqa
+from aws_encryption_sdk.identifiers import Algorithm, CommitmentPolicy, __version__, check_python_version  # noqa
 from aws_encryption_sdk.internal.utils.signature import SignaturePolicy  # noqa
 from aws_encryption_sdk.key_providers.kms import (  # noqa
     DiscoveryAwsKmsMasterKeyProvider,
@@ -36,6 +35,8 @@
     StreamEncryptor,
 )
 
+check_python_version()
+
 
 @attr.s(hash=True)
 class EncryptionSDKClientConfig(object):

src/aws_encryption_sdk/identifiers.py

@@ -11,7 +11,10 @@
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
 """AWS Encryption SDK native data structures for defining implementation-specific characteristics."""
+import datetime
 import struct
+import sys
+import warnings
 from enum import Enum
 
 from cryptography.hazmat.primitives import hashes
@@ -378,3 +381,44 @@ class CommitmentPolicy(Enum):
     FORBID_ENCRYPT_ALLOW_DECRYPT = 0
     REQUIRE_ENCRYPT_ALLOW_DECRYPT = 1
     REQUIRE_ENCRYPT_REQUIRE_DECRYPT = 2
+
+
+class PythonVersionSupport:
+    """Configures Python Version warnings/error messaging"""
+
+    WARN_BELOW_MAJOR = 3
+    WARN_BELOW_MINOR = 6
+    ERROR_BELOW_MAJOR = 3
+    ERROR_BELOW_MINOR = 5
+    ERROR_DATE = datetime.datetime(year=2022, month=1, day=1)
+
+
+def check_python_version(
+    warn_below_major=PythonVersionSupport.WARN_BELOW_MAJOR,
+    warn_below_minor=PythonVersionSupport.WARN_BELOW_MINOR,
+    error_below_major=PythonVersionSupport.ERROR_BELOW_MAJOR,
+    error_below_minor=PythonVersionSupport.ERROR_BELOW_MINOR,
+    error_date=PythonVersionSupport.ERROR_DATE,
+):
+    """Checks that we are on a supported version of Python.
+    Prints an error message to stderr if the Python Version is unsupported and therefore untested.
+    Emits a warning if the Python version will be unsupported.
+    """
+    if datetime.datetime.now() > error_date and (
+        sys.version_info.major < error_below_major or sys.version_info.minor < error_below_minor
+    ):
+        sys.stderr.write(
+            "ERROR: Python {} is not supported by the aws-encryption-sdk! ".format(
+                ".".join(map(str, [sys.version_info.major, sys.version_info.minor]))
+            )
+            + "Please upgrade to Python {} or higher.".format(".".join(map(str, [warn_below_major, warn_below_minor])))
+        )
+        return
+    if sys.version_info.major < warn_below_major or sys.version_info.minor < warn_below_minor:
+        warnings.warn(
+            "Python {} support will be removed in a future release. ".format(
+                ".".join(map(str, [sys.version_info.major, sys.version_info.minor]))
+            )
+            + "Please upgrade to Python {} or higher.".format(".".join(map(str, [warn_below_major, warn_below_minor]))),
+            DeprecationWarning,
+        )

test/unit/test_check_python_version.py

@@ -0,0 +1,62 @@
+# Copyright 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+# http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+"""Unit test suite for ensuring the Python Runtime is supported."""
+import datetime
+import sys
+
+import mock
+import pytest
+
+from aws_encryption_sdk import check_python_version
+from aws_encryption_sdk.identifiers import PythonVersionSupport
+
+pytestmark = [pytest.mark.unit, pytest.mark.local]
+
+
+class TestBeforeErrorDate:
+    def test_happy_version(self):
+        with mock.patch.object(sys, "version_info") as v_info:
+            v_info.major = PythonVersionSupport.WARN_BELOW_MAJOR
+            v_info.minor = PythonVersionSupport.WARN_BELOW_MINOR
+            with pytest.warns(None) as record:
+                check_python_version(error_date=datetime.datetime.now() + datetime.timedelta(days=1))
+            assert len(record) == 0
+
+    def test_below_warn(self):
+        with mock.patch.object(sys, "version_info") as v_info:
+            v_info.major = PythonVersionSupport.WARN_BELOW_MAJOR - 1
+            v_info.minor = PythonVersionSupport.WARN_BELOW_MINOR
+            with pytest.warns(DeprecationWarning):
+                check_python_version(error_date=datetime.datetime.now() + datetime.timedelta(days=1))
+
+
+class TestAfterErrorDate:
+    def test_happy_version(self, capsys):
+        with mock.patch.object(sys, "version_info") as v_info:
+            v_info.major = PythonVersionSupport.WARN_BELOW_MAJOR
+            v_info.minor = PythonVersionSupport.WARN_BELOW_MINOR
+            with pytest.warns(None) as record:
+                check_python_version(error_date=datetime.datetime.now() - datetime.timedelta(days=1))
+            assert len(record) == 0
+            captured = capsys.readouterr().err
+            assert "ERROR" not in captured
+
+    def test_below_error(self, capsys):
+        with mock.patch.object(sys, "version_info") as v_info:
+            v_info.major = PythonVersionSupport.ERROR_BELOW_MAJOR
+            v_info.minor = PythonVersionSupport.ERROR_BELOW_MINOR - 1
+            with pytest.warns(None) as record:
+                check_python_version(error_date=datetime.datetime.now() - datetime.timedelta(days=1))
+            assert len(record) == 0
+            captured = capsys.readouterr().err
+            assert "ERROR" in captured