fix: skip Python binary validation when pip is not used (#678)

aws_lambda_builders/workflows/python_pip/workflow.py

@@ -6,6 +6,7 @@
 
 from aws_lambda_builders.actions import CleanUpAction, CopySourceAction, LinkSourceAction
 from aws_lambda_builders.path_resolver import PathResolver
+from aws_lambda_builders.validator import RuntimeValidator
 from aws_lambda_builders.workflow import BaseWorkflow, BuildDirectory, BuildInSourceSupport, Capability
 from aws_lambda_builders.workflows.python_pip.validator import PythonRuntimeValidator
 
@@ -78,6 +79,8 @@ def __init__(self, source_dir, artifacts_dir, scratch_dir, manifest_path, runtim
         if osutils is None:
             osutils = OSUtils()
 
+        self._use_pip = False
+
         if not self.download_dependencies and not self.dependencies_dir:
             LOG.info(
                 "download_dependencies is False and dependencies_dir is None. Copying the source files into the "
@@ -92,6 +95,7 @@ def __init__(self, source_dir, artifacts_dir, scratch_dir, manifest_path, runtim
 
         # If a requirements.txt exists, run pip builder before copy action.
         if self.download_dependencies:
+            self._use_pip = True
             if self.dependencies_dir:
                 # clean up the dependencies folder before installing
                 self._actions.append(CleanUpAction(self.dependencies_dir))
@@ -161,4 +165,6 @@ def _should_create_parent_packages(self):
         return False
 
     def get_validators(self):
+        if not self._use_pip:
+            return [RuntimeValidator(runtime=self.runtime, architecture=self.architecture)]
         return [PythonRuntimeValidator(runtime=self.runtime, architecture=self.architecture)]

tests/integration/workflows/python_pip/test_python_pip.py

@@ -303,6 +303,39 @@ def test_must_log_warning_if_requirements_not_found(self):
             "requirements.txt file not found. Continuing the build without dependencies."
         )
 
+    def test_build_succeeds_with_mismatched_runtime_when_no_requirements(self):
+        """
+        When no requirements.txt exists, build should succeed even if the target runtime
+        binary validation would fail (issue #678). The base RuntimeValidator is used
+        which only checks if the runtime is supported, not if the binary exists.
+        """
+        # Mock PythonRuntimeValidator to always fail - simulating missing Python binary
+        with mock.patch(
+            "aws_lambda_builders.workflows.python_pip.workflow.PythonRuntimeValidator"
+        ) as mock_validator_class:
+            mock_validator = mock.Mock()
+            mock_validator.validate.side_effect = Exception("Python binary not found")
+            mock_validator_class.return_value = mock_validator
+
+            # This should succeed because without requirements.txt, we use base RuntimeValidator
+            # not PythonRuntimeValidator
+            self.builder.build(
+                self.source_dir,
+                self.artifacts_dir,
+                self.scratch_dir,
+                os.path.join("non", "existent", "manifest"),
+                runtime=self.runtime,
+                experimental_flags=self.experimental_flags,
+            )
+
+        # Should just copy source files
+        expected_files = self.test_data_files
+        output_files = set(os.listdir(self.artifacts_dir))
+        self.assertEqual(expected_files, output_files)
+
+        # Verify PythonRuntimeValidator was never instantiated (we used base RuntimeValidator)
+        mock_validator_class.assert_not_called()
+
     @skipIf(IS_WINDOWS, "Skip in windows tests")
     def test_without_download_dependencies_with_dependencies_dir(self):
         source_dir = os.path.join(self.source_dir, "local-dependencies")

tests/unit/workflows/python_pip/test_workflow.py

@@ -5,6 +5,7 @@
 
 from aws_lambda_builders.actions import CopySourceAction, CleanUpAction, LinkSourceAction
 from aws_lambda_builders.path_resolver import PathResolver
+from aws_lambda_builders.validator import RuntimeValidator
 from aws_lambda_builders.workflows.python_pip.utils import OSUtils, EXPERIMENTAL_FLAG_BUILD_PERFORMANCE
 from aws_lambda_builders.workflows.python_pip.validator import PythonRuntimeValidator
 from aws_lambda_builders.workflows.python_pip.workflow import PythonPipBuildAction, PythonPipWorkflow
@@ -60,6 +61,41 @@ def test_workflow_validator(self):
         for validator in self.workflow.get_validators():
             self.assertTrue(isinstance(validator, PythonRuntimeValidator))
 
+    def test_workflow_validator_without_requirements_skips_python_validation(self):
+        """When no requirements.txt exists, should use base RuntimeValidator (no Python binary check)."""
+        self.osutils_mock.file_exists.return_value = False
+        self.workflow = PythonPipWorkflow(
+            "source",
+            "artifacts",
+            "scratch_dir",
+            "manifest",
+            runtime="python3.12",
+            osutils=self.osutils_mock,
+            experimental_flags=self.experimental_flags,
+        )
+        validators = self.workflow.get_validators()
+        self.assertEqual(len(validators), 1)
+        self.assertIsInstance(validators[0], RuntimeValidator)
+        self.assertNotIsInstance(validators[0], PythonRuntimeValidator)
+
+    def test_workflow_validator_without_download_dependencies_skips_python_validation(self):
+        """When download_dependencies=False, should use base RuntimeValidator (no Python binary check)."""
+        self.osutils_mock.file_exists.return_value = True
+        self.workflow = PythonPipWorkflow(
+            "source",
+            "artifacts",
+            "scratch_dir",
+            "manifest",
+            runtime="python3.12",
+            osutils=self.osutils_mock,
+            download_dependencies=False,
+            experimental_flags=self.experimental_flags,
+        )
+        validators = self.workflow.get_validators()
+        self.assertEqual(len(validators), 1)
+        self.assertIsInstance(validators[0], RuntimeValidator)
+        self.assertNotIsInstance(validators[0], PythonRuntimeValidator)
+
     def test_workflow_resolver(self):
         for resolver in self.workflow.get_resolvers():
             self.assertTrue(isinstance(resolver, PathResolver))