Operations can now be called from the spec by operationId

Intended usage is this::

   spec = OpenAPI(spec_yaml)
   result = spec.call_getLinodeInstances(security={"personalAccessToken": token})

This uses a custom __getattribute__ to convert all attributes started
with call_ to an OperationCallable configured with the (first) base_url
it finds such that it is immediately called with the given arguments.

openapi/openapi.py

@@ -7,7 +7,8 @@ class OpenAPI(ObjectBase):
 
     .. _the spec: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#openapi-object
     """
-    __slots__ = ['openapi','info','servers','paths','components','security','tags','externalDocs']
+    __slots__ = ['openapi','info','servers','paths','components','security','tags',
+                 'externalDocs','_operation_map']
     required_fields=['openapi','info','paths']
 
     def __init__(self, raw_document):
@@ -26,7 +27,7 @@ def _parse_data(self):
         """
         Implementation of :any:`ObjectBase._parse_data`
         """
-        self._required_fields('openapi', 'info', 'paths')
+        self._operation_map = {}
 
         self.openapi = self._get('openapi', str)
         self.info = self._get('info', 'Info')
@@ -36,3 +37,34 @@ def _parse_data(self):
         self.security = self._get('security', dict)
         self.tags = self._get('tags', dict)
         self.externalDocs = self._get('externalDocs', dict)
+
+    def _get_callable(self, operation):
+        """
+        TODO - explain this
+        """
+        base_url = self.servers[0].url
+
+        return OperationCallable(operation, base_url)
+
+    def __getattribute__(self, attr):
+        """
+        TODO - describe what this does
+        """
+        if attr.startswith('call_'):
+            _, operationId = attr.split('_', 1)
+            if operationId in self._operation_map:
+                return self._get_callable(self._operation_map[operationId].request)
+            else:
+                raise AttributeError('{} has no operation {}'.format(
+                    self.info.title, operationId))
+
+        return object.__getattribute__(self, attr)
+
+
+class OperationCallable:
+    def __init__(self, operation, base_url):
+        self.operation = operation
+        self.base_url = base_url
+
+    def __call__(self, *args, **kwargs):
+        return self.operation(self.base_url, *args, **kwargs)

openapi/paths.py

@@ -100,6 +100,11 @@ def _parse_data(self):
         self.servers = self._get('servers', ['Server'], is_list=True)
         raw_servers = self._get('servers', list)
 
+        # gather all operations into the spec object
+        if self.operationId is not None:
+            # TODO - how to store without an operationId?
+            self._root._operation_map[self.operationId] = self
+
     def request(self, base_url, security={}, data=None):
         """
         Sends an HTTP request as described by this Path