(Config YAML) Add support for always dumping default fields

@register_config(always_dump='field names || *')

ovgenpy/config.py

@@ -1,4 +1,5 @@
 from io import StringIO
+from typing import ClassVar
 
 from dataclasses import dataclass, fields
 from ruamel.yaml import yaml_object, YAML
@@ -22,59 +23,84 @@ class MyYAML(YAML):
 yaml = MyYAML()
 
 
-class OvgenError(Exception):
+def register_config(cls=None, *, always_dump: str = ''):
-    pass
-
-
-def __getstate__(self):
-    """ Returns all non-default fields. """
-    state = {}
-    cls = type(self)
-
-    for field in fields(self):
-        name = field.name
-        value = getattr(self, name)
-        default = getattr(cls, name, object())
-
-        if value != default:
-            state[name] = value
-
-    return state
-
-
-def __setstate__(self, state):
-    """ Checks that all fields match their correct types. """
-    self.__dict__.update(state)
-    for field in fields(self):
-        key = field.name
-        value = getattr(self, key)
-        typ = field.type
-
-        if not isinstance(value, typ):
-            name = type(self).__name__
-            raise OvgenError(f'{name}.{key} was supplied {repr(value)}, should be of type {typ.__name__}')
-
-    if hasattr(self, '__post_init__'):
-        self.__post_init__()
-
-
-def register_config(cls):
     """ Marks class as @dataclass, and enables YAML dumping (excludes default fields).
 
     dataclasses.dataclass is compatible with yaml.register_class.
     typing.NamedTuple is incompatible.
     """
 
+    def decorator(cls: type):
+        cls.__getstate__ = _ConfigMixin.__getstate__
+        cls.__setstate__ = _ConfigMixin.__setstate__
+        cls.always_dump = always_dump
+
+        # https://stackoverflow.com/a/51497219/2683842
+        # YAML().register_class(cls) works... on versions more recent than 2018-07-12.
+        return yaml_object(yaml)(
+            dataclass(cls)
+        )
+
+    if cls is not None:
+        return decorator(cls)
+    else:
+        return decorator
+
+    # __init__-less non-dataclasses are also compatible with yaml.register_class.
+
+
+@dataclass()
+class _ConfigMixin:
+    """
+    Class is unused. __getstate__ and __setstate__ are assigned into other classes.
+    Ideally I'd use inheritance, but @yaml_object and @dataclass rely on decorators,
+    and I want @register_config to Just Work and not need inheritance.
+    """
+    always_dump: ClassVar[str]
+
     # SafeRepresenter.represent_yaml_object() uses __getstate__ to dump objects.
-    cls.__getstate__ = __getstate__
+    def __getstate__(self):
+        """ Returns all fields with non-default value, or appeear in
+        self.always_dump. """
+
+        always_dump = set(self.always_dump.split())
+        dump_all = ('*' in always_dump)
+
+        state = {}
+        cls = type(self)
+
+        for field in fields(self):
+            name = field.name
+            value = getattr(self, name)
+
+            if dump_all or name in always_dump:
+                state[name] = value
+                continue
+
+            default = getattr(cls, name, object())
+            if value != default:
+                state[name] = value
+
+        return state
+
     # SafeConstructor.construct_yaml_object() uses __setstate__ to load objects.
-    cls.__setstate__ = __setstate__
+    def __setstate__(self, state):
+        """ Checks that all fields match their correct types. """
+        self.__dict__.update(state)
+        for field in fields(self):
+            key = field.name
+            value = getattr(self, key)
+            typ = field.type
 
-    # https://stackoverflow.com/a/51497219/2683842
+            if not isinstance(value, typ):
-    # YAML().register_class(cls) works... on versions more recent than 2018-07-12.
+                name = type(self).__name__
-    return yaml_object(yaml)(
+                raise OvgenError(f'{name}.{key} was supplied {repr(value)}, should be of type {typ.__name__}')
-        dataclass(cls)
+
-    )
+        if hasattr(self, '__post_init__'):
+            self.__post_init__()
+
+
+class OvgenError(Exception):
+    pass
 
 
-# __init__-less non-dataclasses are also compatible with yaml.register_class.

tests/test_config.py

@@ -34,19 +34,43 @@ def test_yaml_object():
     assert s == '!Bar {}\n'
 
 
-def test_dump_exclude_defaults():
+def test_dump_defaults():
     @register_config
-    class DefaultConfig:
+    class Config:
         a: str = 'a'
         b: str = 'b'
 
-    s = yaml.dump(DefaultConfig('alpha'))
+    s = yaml.dump(Config('alpha'))
-    assert 'b:' not in s
     assert s == '''\
-!DefaultConfig
+!Config
 a: alpha
 '''
 
+    @register_config(always_dump='a b')
+    class Config:
+        a: str = 'a'
+        b: str = 'b'
+        c: str = 'c'
+
+    s = yaml.dump(Config())
+    assert s == '''\
+!Config
+a: a
+b: b
+'''
+
+    @register_config(always_dump='*')
+    class Config:
+        a: str = 'a'
+        b: str = 'b'
+
+    s = yaml.dump(Config())
+    assert s == '''\
+!Config
+a: a
+b: b
+'''
+
 
 def test_load_type_checking():
     @register_config