HOT str_replace to use string.replace, not string.Template

str_replace uses python templates, whereas Fn::Replace uses python
string.replace.

During the original review for Fn::Replace, python templates were
decided against because $ would often need double-escaping in shell scripts.
https://review.openstack.org/#/c/31736/

Having different behaviours between Fn::Replace and str_replace will
add complication for users migrating existing templates to HOT.

Another advantage of using straight string replacement is seen when
the template generates a executable script. In this case it is generally
possible to write a template that can also be executed directly in a
dev/test environment. This would often not be possible if the template
format required placeholders to be prefixed with a $.

Whatever behaviour exists when Havana is release will have to be
supported indefinitely so now is the time to decide if this is going
to be fixed.

Closes-Bug: #1228640
Change-Id: I72879b374a3c61dfe0e4004251ab709d914f2e25

doc/source/template_guide/hot_spec.rst

@@ -464,8 +464,8 @@ str_replace
 -----------
 The *str_replace* function allows for dynamically constructing strings by
 providing a template string with placeholders and a list of mappings to assign
-values to those placeholders at runtime. The functionality of this function is
-similar to that of Python Template strings.
+values to those placeholders at runtime. The placeholders are replaced with
+mapping values wherever a mapping key exactly matches a placeholder.
 The syntax of the str_replace function is as follows:
 
 ::
@@ -499,7 +499,7 @@ section of a template to build a URL for logging into a deployed application.
       description: The URL to log into the deployed application
       value:
         str_replace:
-          template: http://$host/MyApplication
+          template: http://host/MyApplication
           params:
             host: { get_attr: [ my_instance, PublicIp ] }
 
@@ -528,7 +528,7 @@ like scripts for initializing compute instances as shown in the example below:
               mysqladmin -u root password $db_rootpassword
               # do more things ...
             params:
-              db_rootpassword: { get_param: DBRootPassword }
+              $db_rootpassword: { get_param: DBRootPassword }
 
 In the example above, one can imagine that MySQL is being configured on a
 compute instance and the root password is going to be set based on a user

heat/engine/hot.py

@@ -12,8 +12,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import string
-
 from heat.common import exception
 from heat.engine import template
 from heat.engine.parameters import ParamSchema
@@ -260,7 +258,7 @@ class HOTemplate(template.Template):
                     raise KeyError()
             except KeyError:
                 example = ('''str_replace:
-                  template: This is $var1 template $var2
+                  template: This is var1 template var2
                   params:
                     var1: a
                     var2: string''')
@@ -271,13 +269,10 @@ class HOTemplate(template.Template):
             if not isinstance(params, dict):
                 raise TypeError(
                     '"params" parameter must be a dictionary')
-            if isinstance(args, list):
-                for key in params.iterkeys():
-                    value = params.get(key, '')
-                    text = text.replace(key, value)
-                return text
-
-            return string.Template(text).safe_substitute(params)
+            for key in params.iterkeys():
+                value = params.get(key, '')
+                text = text.replace(key, value)
+            return text
 
         match_str_replace = lambda k, v: k in ['str_replace', 'Fn::Replace']
         return template._resolve(match_str_replace,

heat/tests/test_hot.py

@@ -269,7 +269,7 @@ class HOTemplateTest(HeatTestCase):
     def test_str_replace(self):
         """Test str_replace function."""
 
-        snippet = {'str_replace': {'template': 'Template $var1 string $var2',
+        snippet = {'str_replace': {'template': 'Template var1 string var2',
                                    'params': {'var1': 'foo', 'var2': 'bar'}}}
         snippet_resolved = 'Template foo string bar'
 
@@ -297,7 +297,7 @@ class HOTemplateTest(HeatTestCase):
         validate that we get a TypeError.
         """
 
-        snippet = {'str_replace': [{'template': 'Template $var1 string $var2'},
+        snippet = {'str_replace': [{'template': 'Template var1 string var2'},
                                    {'params': {'var1': 'foo', 'var2': 'bar'}}]}
 
         tmpl = parser.Template(hot_tpl_empty)
@@ -312,14 +312,14 @@ class HOTemplateTest(HeatTestCase):
         a KeyError.
         """
 
-        snippet = {'str_replace': {'tmpl': 'Template $var1 string $var2',
+        snippet = {'str_replace': {'tmpl': 'Template var1 string var2',
                                    'params': {'var1': 'foo', 'var2': 'bar'}}}
 
         tmpl = parser.Template(hot_tpl_empty)
 
         self.assertRaises(KeyError, tmpl.resolve_replace, snippet)
 
-        snippet = {'str_replace': {'tmpl': 'Template $var1 string $var2',
+        snippet = {'str_replace': {'tmpl': 'Template var1 string var2',
                                    'parms': {'var1': 'foo', 'var2': 'bar'}}}
 
         self.assertRaises(KeyError, tmpl.resolve_replace, snippet)
@@ -339,7 +339,7 @@ class HOTemplateTest(HeatTestCase):
 
         self.assertRaises(TypeError, tmpl.resolve_replace, snippet)
 
-        snippet = {'str_replace': {'template': 'Template $var1 string $var2',
+        snippet = {'str_replace': {'template': 'Template var1 string var2',
                                    'params': ['var1', 'foo', 'var2', 'bar']}}
 
         self.assertRaises(TypeError, tmpl.resolve_replace, snippet)