Add default lambda handler, for zero-code change instrumentation

Author: DarcyRaynerDD

datadog_lambda/handler.py

@@ -0,0 +1,22 @@
+from __future__ import absolute_import
+from importlib import import_module
+import os
+from datadog_lambda.wrapper import datadog_lambda_wrapper
+
+
+class HandlerError(Exception):
+    pass
+
+
+path = os.environ.get("DATADOG_USER_HANDLER", None)
+if path is None:
+    raise HandlerError(
+        "DATADOG_USER_HANDLER is not defined. Can't use prebuilt datadog handler"
+    )
+parts = path.rsplit(".", 1)
+if len(parts) != 2:
+    raise HandlerError("Value %s for DATADOG_USER_HANDLER has invalid format." % path)
+
+(mod_name, handler_name) = parts
+handler_module = import_module(mod_name)
+handler = datadog_lambda_wrapper(getattr(handler_module, handler_name))