fix: skip Python binary validation when pip is not used (#678) (#830)

When no requirements.txt exists or download_dependencies=False,
the workflow only copies files and doesn't run pip. In these cases,
skip PythonRuntimeValidator and use the base RuntimeValidator instead.

This allows builds to succeed even when the target Python runtime
isn't installed locally, as long as no dependencies need to be installed.

Co-authored-by: Reed Hamilton <reedham@amazon.com>

Author: sriram-mv

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))