By defining a main function here, and including it ahead of the boilerplate insertion symbol, tracebacks are

now accurate with respect to the main function, but may include lines not in the original file.  A lot better
than before, where they were offset.

library/slurp

@@ -19,22 +19,25 @@
 
 import base64
 
-# this is magic, see lib/ansible/module_common.py
-#<<INCLUDE_ANSIBLE_MODULE_COMMON>>
-
-module = AnsibleModule(
-    argument_spec = dict(
-        src = dict(required=True),
+def main():
+    module = AnsibleModule(
+        argument_spec = dict(
+            src = dict(required=True),
+        )
     )
-)
-source = module.params['src']
+    source = module.params['src']
+
+    if not os.path.exists(source):
+        module.fail_json(msg="file not found: %s" % source)
+    if not os.access(source, os.R_OK):
+        module.fail_json(msg="file is not readable: %s" % source)
 
-if not os.path.exists(source):
-    module.fail_json(msg="file not found: %s" % source)
-if not os.access(source, os.R_OK):
-    module.fail_json(msg="file is not readable: %s" % source)
+    data = base64.b64encode(file(source).read())
 
-data = base64.b64encode(file(source).read())
+    module.exit_json(content=data, encoding='base64')
+
+# this is magic, see lib/ansible/module_common.py
+#<<INCLUDE_ANSIBLE_MODULE_COMMON>>
 
-module.exit_json(content=data, encoding='base64')
+main()