Implement fallback methods. Closes #11

configspec/manager.py

@@ -10,6 +10,32 @@ class ConfigManager():
         self.root_config = {}  # validated config
         self.confspecs = {}
         self.frozen_config = {}  # validated config to reapply each load
+        self._saved_state = {}
+
+    def save_fallback(self):
+        """
+        Save the current state of the ConfigManager for future restoration with ``fallback()``.
+        Includes the loaded config source, the validated config, any added config specifications,
+        and any frozen values.
+        """
+        self._saved_state["config_source"] = deepcopy(self.config_source)
+        self._saved_state["root_config"] = deepcopy(self.root_config)
+        self._saved_state["confspecs"] = deepcopy(self.confspecs)
+        self._saved_state["frozen_config"] = deepcopy(self.frozen_config)
+
+    def fallback(self):
+        """
+        Restore the state of the ConfigManager to what is was when ``save_fallback()`` was last
+        called. Includes the loaded config source, the validated config, any added config
+        specifications, and any frozen values.
+        """
+        if not all(k in self._saved_state for k in ("config_source", "root_config",
+                                                    "confspecs", "frozen_config")):
+            raise Exception("Can't fallback ConfigManager without calling save_fallback() first!")
+        self.config_source = self._saved_state["config_source"]
+        self.root_config = self._saved_state["root_config"]
+        self.confspecs = self._saved_state["confspecs"]
+        self.frozen_config = self._saved_state["frozen_config"]
 
     @staticmethod
     def _get_source(source):