Create static tags once on import. (#460)

* Create lambda layer tag only once.

* Only create runtime tag once.

* Create library version tag just once.

* Avoid extra list allocations when creating tags.

* Cleaned test.

* Linting.

Author: purple4reina

datadog_lambda/metric.py

@@ -9,7 +9,7 @@
 import logging
 
 from datadog_lambda.extension import should_use_extension
-from datadog_lambda.tags import get_enhanced_metrics_tags, tag_dd_lambda_layer
+from datadog_lambda.tags import get_enhanced_metrics_tags, dd_lambda_layer_tag
 from datadog_lambda.api import init_api
 
 logger = logging.getLogger(__name__)
@@ -50,7 +50,8 @@ def lambda_metric(metric_name, value, timestamp=None, tags=None, force_async=Fal
     and always use the layer to send metrics to the extension
     """
     flush_to_logs = os.environ.get("DD_FLUSH_TO_LOG", "").lower() == "true"
-    tags = tag_dd_lambda_layer(tags)
+    tags = [] if tags is None else list(tags)
+    tags.append(dd_lambda_layer_tag)
 
     if should_use_extension:
         logger.debug(

datadog_lambda/tags.py

@@ -4,23 +4,10 @@
 from datadog_lambda.cold_start import get_cold_start_tag
 
 
-def _format_dd_lambda_layer_tag():
-    """
-    Formats the dd_lambda_layer tag, e.g., 'dd_lambda_layer:datadog-python39_1'
-    """
-    major, minor = sys.version_info[0], sys.version_info[1]
-    return f"dd_lambda_layer:datadog-python{major}{minor}_{__version__}"
-
-
-def tag_dd_lambda_layer(tags):
-    """
-    Used by lambda_metric to insert the dd_lambda_layer tag
-    """
-    dd_lambda_layer_tag = _format_dd_lambda_layer_tag()
-    if tags:
-        return tags + [dd_lambda_layer_tag]
-    else:
-        return [dd_lambda_layer_tag]
+_major, _minor = sys.version_info[0], sys.version_info[1]
+dd_lambda_layer_tag = f"dd_lambda_layer:datadog-python{_major}{_minor}_{__version__}"
+runtime_tag = f"runtime:python{_major}.{_minor}"
+library_version_tag = f"datadog_lambda:v{__version__}"
 
 
 def parse_lambda_tags_from_arn(lambda_context):
@@ -30,12 +17,12 @@ def parse_lambda_tags_from_arn(lambda_context):
             ex: lambda_context.arn = arn:aws:lambda:us-east-1:123597598159:function:my-lambda:1
     """
     # Set up flag for extra testing to distinguish between a version or alias
-    hasAlias = False
+    has_alias = False
     # Cap the number of times to spli
     split_arn = lambda_context.invoked_function_arn.split(":")
 
     if len(split_arn) > 7:
-        hasAlias = True
+        has_alias = True
         _, _, _, region, account_id, _, function_name, alias = split_arn
     else:
         _, _, _, region, account_id, _, function_name = split_arn
@@ -48,7 +35,7 @@ def parse_lambda_tags_from_arn(lambda_context):
     ]
 
     # Check if we have a version or alias
-    if hasAlias:
+    if has_alias:
         # If $Latest, drop the $ for datadog tag convention. A lambda alias can't start with $
         if alias.startswith("$"):
             alias = alias[1:]
@@ -66,25 +53,14 @@ def parse_lambda_tags_from_arn(lambda_context):
     return tags
 
 
-def get_runtime_tag():
-    """Get the runtime tag from the current Python version"""
-    major, minor = sys.version_info[0], sys.version_info[1]
-    return f"runtime:python{major}.{minor}"
-
-
-def get_library_version_tag():
-    """Get datadog lambda library tag"""
-    return f"datadog_lambda:v{__version__}"
-
-
 def get_enhanced_metrics_tags(lambda_context):
     """Get the list of tags to apply to enhanced metrics"""
-    return parse_lambda_tags_from_arn(lambda_context) + [
-        get_cold_start_tag(),
-        f"memorysize:{lambda_context.memory_limit_in_mb}",
-        get_runtime_tag(),
-        get_library_version_tag(),
-    ]
+    tags = parse_lambda_tags_from_arn(lambda_context)
+    tags.append(get_cold_start_tag())
+    tags.append(f"memorysize:{lambda_context.memory_limit_in_mb}")
+    tags.append(runtime_tag)
+    tags.append(library_version_tag)
+    return tags
 
 
 def check_if_number(alias):

tests/test_metric.py

@@ -10,7 +10,7 @@
 from datadog_lambda.metric import lambda_metric
 from datadog_lambda.api import decrypt_kms_api_key, KMS_ENCRYPTION_CONTEXT_KEY
 from datadog_lambda.thread_stats_writer import ThreadStatsWriter
-from datadog_lambda.tags import _format_dd_lambda_layer_tag
+from datadog_lambda.tags import dd_lambda_layer_tag
 
 
 class TestLambdaMetric(unittest.TestCase):
@@ -23,12 +23,13 @@ def test_lambda_metric_tagged_with_dd_lambda_layer(self):
         lambda_metric("test", 1)
         lambda_metric("test", 1, 123, [])
         lambda_metric("test", 1, tags=["tag1:test"])
-        expected_tag = _format_dd_lambda_layer_tag()
         self.mock_metric_lambda_stats.distribution.assert_has_calls(
             [
-                call("test", 1, timestamp=None, tags=[expected_tag]),
-                call("test", 1, timestamp=123, tags=[expected_tag]),
-                call("test", 1, timestamp=None, tags=["tag1:test", expected_tag]),
+                call("test", 1, timestamp=None, tags=[dd_lambda_layer_tag]),
+                call("test", 1, timestamp=123, tags=[dd_lambda_layer_tag]),
+                call(
+                    "test", 1, timestamp=None, tags=["tag1:test", dd_lambda_layer_tag]
+                ),
             ]
         )
 
@@ -37,9 +38,8 @@ def test_lambda_metric_tagged_with_dd_lambda_layer(self):
     def test_lambda_metric_flush_to_log_with_extension(self):
         os.environ["DD_FLUSH_TO_LOG"] = "True"
         lambda_metric("test", 1)
-        expected_tag = _format_dd_lambda_layer_tag()
         self.mock_metric_lambda_stats.distribution.assert_has_calls(
-            [call("test", 1, timestamp=None, tags=[expected_tag])]
+            [call("test", 1, timestamp=None, tags=[dd_lambda_layer_tag])]
         )
         del os.environ["DD_FLUSH_TO_LOG"]
 

tests/test_tags.py

@@ -3,7 +3,7 @@
 from unittest.mock import patch, MagicMock
 
 
-from datadog_lambda.tags import parse_lambda_tags_from_arn, get_runtime_tag
+from datadog_lambda.tags import parse_lambda_tags_from_arn
 
 
 def get_mock_context(
@@ -63,6 +63,3 @@ def test_parse_lambda_tags_from_arn_alias(self):
                 "resource:swf-hello-test:my_alias-1",
             ],
         )
-
-    def test_get_runtime_tag(self):
-        self.assertEqual(get_runtime_tag(), "runtime:python3.12")

tests/test_wrapper.py

@@ -66,25 +66,27 @@ def setUp(self):
         self.mock_get_cold_start_tag.return_value = "cold_start:true"
         self.addCleanup(patcher.stop)
 
-        patcher = patch("sys.version_info", (3, 9, 10))
-        self.mock_python_version_tuple = patcher.start()
+        patcher = patch("datadog_lambda.tags.runtime_tag", "runtime:python3.9")
+        self.mock_runtime_tag = patcher.start()
         self.addCleanup(patcher.stop)
 
         patcher = patch("datadog_lambda.metric.write_metric_point_to_stdout")
         self.mock_write_metric_point_to_stdout = patcher.start()
         self.addCleanup(patcher.stop)
 
-        patcher = patch("datadog_lambda.tags.get_library_version_tag")
-        self.mock_format_dd_lambda_layer_tag = patcher.start()
+        patcher = patch(
+            "datadog_lambda.tags.library_version_tag", "datadog_lambda:v6.6.6"
+        )
         # Mock the layer version so we don't have to update tests on every version bump
-        self.mock_format_dd_lambda_layer_tag.return_value = "datadog_lambda:v6.6.6"
+        self.mock_library_version_tag = patcher.start()
+        self.addCleanup(patcher.stop)
 
-        patcher = patch("datadog_lambda.tags._format_dd_lambda_layer_tag")
-        self.mock_format_dd_lambda_layer_tag = patcher.start()
-        # Mock the layer version so we don't have to update tests on every version bump
-        self.mock_format_dd_lambda_layer_tag.return_value = (
-            "dd_lambda_layer:datadog-python39_X.X.X"
+        patcher = patch(
+            "datadog_lambda.metric.dd_lambda_layer_tag",
+            "dd_lambda_layer:datadog-python39_X.X.X",
         )
+        # Mock the layer version so we don't have to update tests on every version bump
+        self.mock_dd_lambda_layer_tag = patcher.start()
         self.addCleanup(patcher.stop)
 
     def test_datadog_lambda_wrapper(self):