Warn people not to edit the generated README.md. Improve the placehol…

…der handling.

example/README.md

@@ -1,3 +1,5 @@
+<!-- NOTE: This file is generated from skewer.yaml.  Do not edit it directly. -->
+
 # Skupper Hello World
 
 [![main](https://github.com/skupperproject/skewer/actions/workflows/main.yaml/badge.svg)](https://github.com/skupperproject/skewer/actions/workflows/main.yaml)
@@ -32,12 +34,10 @@ across cloud providers, data centers, and edge sites.
 
 An overview
 
-
 ## Prerequisites
 
 Some prerequisites
 
-
 ## Step 1: Install the Skupper command-line tool
 
 This example uses the Skupper command-line tool to deploy Skupper.
@@ -249,7 +249,6 @@ _**West:**_
 
 ~~~ shell
 if [ -n "${SKEWER_FAIL}" ]; then expr 1 / 0; fi
-
 ~~~
 
 ## Step 7: Expose the backend
@@ -323,7 +322,6 @@ navigating to `http://<external-ip>:8080/` in your browser.
 To remove Skupper and the other resources from this exercise, use
 the following commands:
 
-
 And more!
 
 _**West:**_
@@ -343,18 +341,14 @@ kubectl delete deployment/backend
 
 ## Summary
 
-
-
 More summary
 
-
 ## Next steps
 
 Check out the other [examples][examples] on the Skupper website.
 
 More steps
 
-
 ## About this example
 
 This example was produced using [Skewer][skewer], a library for

python/skewer/main.py

@@ -312,6 +312,9 @@ def append_section(heading, text):
         out.append(text)
         out.append("")
 
+    out.append("<!-- NOTE: This file is generated from skewer.yaml.  Do not edit it directly. -->")
+    out.append("")
+
     out.append(f"# {model.title}")
     out.append("")
 
@@ -427,23 +430,22 @@ def apply_standard_steps(model):
         del step.data["standard"]
 
         def apply_attribute(name, default=None):
-            value = standard_step_data.get(name, default)
+            standard_value = standard_step_data.get(name, default)
+            value = step.data.get(name, standard_value)
+
+            if is_string(value):
+                if standard_value is not None:
+                    value = value.replace("@default@", str(nvl(standard_value, "")).strip())
 
-            if name in step.data:
-                if name in ("title", "preamble", "postamble"):
-                    if value:
-                        step.data[name] = step.data[name].replace("@default@", value)
-                    else:
-                        step.data[name] = step.data[name].replace("@default@", "")
-            else:
-                if value and name in ("title", "preamble", "postamble"):
-                    for i, site in enumerate([x for _, x in model.sites]):
-                        value = value.replace(f"@site{i}@", site.title)
+                for i, site in enumerate([x for _, x in model.sites]):
+                    value = value.replace(f"@site{i}@", site.title)
 
-                        if site.namespace:
-                            value = value.replace(f"@namespace{i}@", site.namespace)
+                    if site.namespace:
+                        value = value.replace(f"@namespace{i}@", site.namespace)
 
-                step.data[name] = value
+                value = value.strip()
+
+            step.data[name] = value
 
         apply_attribute("name")
         apply_attribute("title")
@@ -521,13 +523,9 @@ def object_property(name, default=None):
     def get(obj):
         value = obj.data.get(name, default)
 
-        try:
-            if default is None:
-                value = value.replace("@default@", "")
-            else:
-                value = value.replace("@default@", default)
-        except AttributeError:
-            pass
+        if is_string(value):
+            value = value.replace("@default@", str(nvl(default, "")).strip())
+            value = value.strip()
 
         return value
 
@@ -550,10 +548,10 @@ class Model:
     subtitle = object_property("subtitle")
     workflow = object_property("workflow", "main.yaml")
     overview = object_property("overview")
-    prerequisites = object_property("prerequisites", standard_text["prerequisites"].strip())
+    prerequisites = object_property("prerequisites", standard_text["prerequisites"])
     summary = object_property("summary")
-    next_steps = object_property("next_steps", standard_text["next_steps"].strip())
-    about_this_example = object_property("about_this_example", standard_text["about_this_example"].strip())
+    next_steps = object_property("next_steps", standard_text["next_steps"])
+    about_this_example = object_property("about_this_example", standard_text["about_this_example"])
 
     def __init__(self, skewer_file, kubeconfigs=[]):
         self.skewer_file = skewer_file