Merge pull request #61 from remind101/add_local_parameters

Local parameters for python

stacker/blueprints/base.py

@@ -3,9 +3,49 @@
 
 from troposphere import Parameter, Template
 
+from ..exceptions import MissingLocalParameterException
+
 logger = logging.getLogger(__name__)
 
 
+def get_local_parameters(parameter_def, parameters):
+    """Gets local parameters from parameter list.
+
+    Given a local parameter definition, and a list of parameters, extract the
+    local parameters, or use a default if provided. If the parameter isn't
+    present, and there is no default, then throw an exception.
+
+    Args:
+        parameter_def (dict): A dictionary of expected/allowed parameters
+            and their defaults. If a parameter is in the list, but does not
+            have a default, it is considered required.
+        parameters (dict): A dictionary of parameters to pull local parameters
+            from.
+
+    Returns:
+        dict: A dictionary of local parameters.
+
+    Raises:
+        MissingLocalParameterException: If a parameter is defined in
+            parameter_def, does not have a default, and does not exist in
+            parameters.
+
+    """
+    local = {}
+
+    for param, attrs in parameter_def.items():
+        try:
+            value = parameters[param]
+        except KeyError:
+            try:
+                value = attrs['default']
+            except KeyError:
+                raise MissingLocalParameterException(param)
+        local[param] = value
+
+    return local
+
+
 class Blueprint(object):
     """Base implementation for dealing with a troposphere template.
 
@@ -23,6 +63,7 @@ def __init__(self, name, context, mappings=None):
         self.mappings = mappings
         self.context = context
         self.outputs = {}
+        self.local_parameters = self.get_local_parameters()
         self.reset_template()
 
     @property
@@ -38,12 +79,21 @@ def required_parameters(self):
                 required.append((k, v))
         return required
 
+    def get_local_parameters(self):
+        local_parameters = getattr(self, 'LOCAL_PARAMETERS', {})
+        return get_local_parameters(local_parameters, self.context.parameters)
+
     def setup_parameters(self):
         t = self.template
-        parameters = getattr(self, 'PARAMETERS')
+        # First look for CF_PARAMETERS, then fall back to regular PARAMETERS
+        # for backwards compatibility.
+        parameters = getattr(self, 'CF_PARAMETERS',
+                             getattr(self, 'PARAMETERS', {}))
+
         if not parameters:
             logger.debug("No parameters defined.")
             return
+
         for param, attrs in parameters.items():
             p = Parameter(param,
                           Type=attrs.get('type'),

stacker/exceptions.py

@@ -9,13 +9,22 @@ class MissingParameterException(Exception):
 
     def __init__(self, parameters, *args, **kwargs):
         self.parameters = parameters
-        message = 'Missing required parameters: %s' % (
+        message = 'Missing required cloudformation parameters: %s' % (
             ', '.join(parameters),
         )
         super(MissingParameterException, self).__init__(message, *args,
                                                         **kwargs)
 
 
+class MissingLocalParameterException(Exception):
+
+    def __init__(self, parameter, *args, **kwargs):
+        self.parameter = parameter
+        message = 'Missing required local parameter: %s' % parameter
+        super(MissingLocalParameterException, self).__init__(message, *args,
+                                                             **kwargs)
+
+
 class OutputDoesNotExist(Exception):
 
     def __init__(self, stack_name, output, *args, **kwargs):

stacker/tests/blueprints/test_base.py

@@ -0,0 +1,29 @@
+import unittest
+
+from stacker.blueprints.base import get_local_parameters
+from stacker.exceptions import MissingLocalParameterException
+
+
+class TestLocalParameters(unittest.TestCase):
+    def test_default_parameter(self):
+        parameter_def = {'Param1': {'default': 0}}
+        parameters = {}
+
+        local = get_local_parameters(parameter_def, parameters)
+        self.assertEquals(local['Param1'], 0)
+
+    def test_missing_required(self):
+        parameter_def = {'Param1': {'default': 0}, 'Param2': {}}
+        parameters = {}
+
+        with self.assertRaises(MissingLocalParameterException) as cm:
+            get_local_parameters(parameter_def, parameters)
+
+        self.assertEquals('Param2', cm.exception.parameter)
+
+    def test_supplied_parameter(self):
+        parameter_def = {'Param1': {'default': 0}, 'Param2': {}}
+        parameters = {'Param1': 1, 'Param2': 2}
+
+        local = get_local_parameters(parameter_def, parameters)
+        self.assertEquals(parameters, local)