improvements to Config

src/ploomber/config.py

@@ -1,3 +1,4 @@
+import warnings
 import abc
 from collections.abc import Mapping
 
@@ -6,6 +7,8 @@
 
 class Config(abc.ABC):
     def __init__(self):
+        self._init_values()
+
         # resolve home directory
         path = self.path()
 
@@ -19,13 +22,13 @@ def __init__(self):
             try:
                 content = yaml.safe_load(text)
                 loaded = True
-            except Exception:
-                # NOTE: show warning?
+            except Exception as e:
+                warnings.warn(str(e))
                 loaded = False
                 content = self._get_data()
 
             if loaded and not isinstance(content, Mapping):
-                # NOTE: show warning?
+                warnings.warn('YAMl not a mapping')
                 content = self._get_data()
 
             self._set_data(content)
@@ -42,6 +45,16 @@ def _set_data(self, data):
             if key in data:
                 setattr(self, key, data[key])
 
+    def _init_values(self):
+        for key in self.__annotations__:
+            name = f'{key}_default'
+            if hasattr(self, name):
+                value = getattr(self, name)()
+                # call __setattr__ on the superclass so we skip the part
+                # where we overwrite the YAML file, here we only want to
+                # set the default values
+                super().__setattr__(key, value)
+
     def _write(self):
         path = self.path()
         data = self._get_data()

tests/test_config.py

@@ -14,6 +14,17 @@ def path(self):
         return Path('myconfig.yaml')
 
 
+class AnotherConfig(Config):
+    uuid: str
+    another: str = 'default'
+
+    def path(self):
+        return Path('another.yaml')
+
+    def uuid_default(self):
+        return 'some-value'
+
+
 def test_stores_defaults(tmp_directory):
     MyConfig()
 
@@ -78,3 +89,23 @@ def test_uses_defaults_if_corrupted(tmp_directory, content):
     assert cfg.number == 42
     assert cfg.string == 'value'
     assert content == {'number': 42, 'string': 'value'}
+
+
+def test_config_with_factory(tmp_directory):
+    cfg = AnotherConfig()
+
+    assert cfg.uuid == 'some-value'
+    assert cfg.another == 'default'
+
+
+def test_factory_keeps_existing_values(tmp_directory):
+    path = Path('another.yaml')
+    values = {'uuid': 'my-uuid', 'another': 'some-value'}
+    path.write_text(yaml.dump(values))
+
+    cfg = AnotherConfig()
+    content = yaml.safe_load(Path('another.yaml').read_text())
+
+    assert cfg.uuid == 'my-uuid'
+    assert cfg.another == 'some-value'
+    assert content == values