Create simple config system

cheuph/euphoria/config.py

@@ -0,0 +1,88 @@
+from typing import Any, Dict
+
+__all__ = ["Config"]
+
+Fields = Dict[str, Any]
+
+class ConfigException(Exception):
+    pass
+
+class Config:
+    @staticmethod
+    def from_tree(tree: Any, prefix: str = "") -> Fields:
+        """
+        This function takes a nested dict using str-s as keys, and converts it
+        to a flat Fields dict. This means that an option's value can't be a
+        dict, and all dicts are expected to only use str-s as keys.
+
+        It uses the '.' character as separator, so {"a":{"b": 1, "c": 2}}
+        becomes {"a.b": 1, "a.c": 2}.
+        """
+
+        result: Fields = {}
+
+        for k, v in tree.items():
+            if not isinstance(k, str):
+                raise ConfigException("Keys must be strings")
+
+            if "." in k:
+                raise ConfigException("Keys may not contain the '.' character")
+
+            name = prefix + k
+
+            if isinstance(v, dict):
+                result.update(Config.from_tree(v, prefix=name+"."))
+            else:
+                result[name] = v
+
+        return result
+
+    @staticmethod
+    def to_tree(fields: Fields) -> Fields:
+        """
+        This function does the opposite of from_tree().
+
+        It uses the '.' character as separator, so {"a.b": 1, "a.c": 2}
+        becomes {"a":{"b": 1, "c": 2}}.
+        """
+
+        result: Any = {}
+
+        for k, v in fields.items():
+            steps = k.split(".")
+
+            subdict = result
+            for step in steps[:-1]:
+                new_subdict = subdict.get(step, {})
+                subdict[step] = new_subdict
+                subdict = new_subdict
+
+            subdict[steps[-1]] = v
+
+        return result
+
+    def __init__(self, default_fields: Fields = {}) -> None:
+        self.default_fields = default_fields
+        self.fields: Fields = {}
+
+    def __getitem__(self, key: str) -> Any:
+        value = self.fields.get(key)
+
+        if value is None:
+            value = self.default_fields.get(key)
+
+        if value is None:
+            raise ConfigException(f"No value for {key} found")
+
+        return value
+
+    def __setitem__(self, key: str, value: Any) -> None:
+        if isinstance(value, dict):
+            raise ConfigException("No dicts allowed")
+        default = self.default_fields.get(key)
+
+        if value == default:
+            if self.fields.get(key)is not None:
+                self.fields.pop(key)
+        else:
+            self.fields[key] = value