Implement skip_if_false field attribute

Author: yukinarit

README.md

@@ -62,6 +62,7 @@ From Json: Hoge(i=10, s='hoge', f=100.0, b=True)
 * Field attributes
     * [Rename](#rename-field)
     * [Skip](#skip-field)
+    * [Skip if value is evaluated as False](#skip-if-value-is-evaluated-as-false)
 
 ### Case conversion
 
@@ -109,6 +110,26 @@ For complete example, please see [./examples/rename.py](./examples/rename.py)
 
 For complete example, please see [./examples/skip.py](./examples/skip.py)
 
+### Skip if value is evaluated as False
+
+```python
+>>> @serialize
+... @dataclass
+... class World:
+...     player: str
+...     enemies: List[str] = field(default_factory=list, metadata={'serde_skip_if_false': True})
+
+>>> world = World('satoshi', ['Rattata', 'Pidgey'])
+>>> to_json(world)
+'{"player": "satoshi", "enemies": ["Rattata", "Pidgey"]}'
+
+>>> world = World('green', [])
+>>> print(to_json(world))
+'{"player": "green"}'
+```
+
+For complete example, please see [./examples/skip.py](./examples/skip.py)
+
 ## Documentation
 
 https://yukinarit.github.io/pyserde/

examples/skip.py

@@ -22,13 +22,26 @@ class Resource:
     metadata: Dict[str, str] = field(default_factory=dict, metadata={'serde_skip': True})
 
 
+@serialize
+@dataclass
+class World:
+    player: str
+    enemies: List[str] = field(default_factory=list, metadata={'serde_skip_if_false': True})
+
+
 def main():
     resources = [
         Resource("Stack Overflow", "b6469c3f31653d281bbbfa6f94d60fea130abe38"),
         Resource("GitHub", "5cb7a0c47e53854cd00e1a968de5abce1c124601", metadata={"headquarters": "San Francisco"}),
     ]
     print(to_json(resources))
 
+    world = World('satoshi', ['Rattata', 'Pidgey'])
+    print(to_json(world))
+
+    world = World('green', [])
+    print(to_json(world))
+
 
 if __name__ == '__main__':
     main()

serde/de.py

@@ -100,7 +100,7 @@ class Deserializer(metaclass=abc.ABCMeta):
     """
 
     @abc.abstractclassmethod
-    def deserialize(self, data, **opts):
+    def deserialize(cls, data, **opts):
         """
         deserialize `data` into an object typically `dict`, `list` or `tuple`.
 
@@ -149,7 +149,7 @@ def from_obj(c: Type[T], o: Any, de: Type[Deserializer] = None, strict=True, **o
     >>>
     """
     if de:
-        o = de().deserialize(o, **opts)
+        o = de.deserialize(o, **opts)
     if o is None:
         v = None
     if is_deserializable(c):

serde/json.py

@@ -7,17 +7,19 @@
 
 
 class JsonSerializer(Serializer):
-    def serialize(self, obj: Any, **opts) -> str:
+    @classmethod
+    def serialize(cls, obj: Any, **opts) -> str:
         return json.dumps(asdict(obj), **opts)
 
 
 class JsonDeserializer(Deserializer):
-    def deserialize(self, s, **opts):
+    @classmethod
+    def deserialize(cls, s, **opts):
         return json.loads(s, **opts)
 
 
-def to_json(obj: Any, cls=JsonSerializer) -> str:
-    return cls().serialize(obj)
+def to_json(obj: Any, cls: Type[JsonSerializer] = JsonSerializer) -> str:
+    return cls.serialize(obj)
 
 
 def from_json(c: Type[T], s: str, de: Type[Deserializer] = JsonDeserializer, **opts) -> T:

serde/msgpack.py

@@ -9,12 +9,14 @@
 
 
 class MsgPackSerializer(Serializer):
-    def serialize(self, obj: Any, **opts) -> str:
+    @classmethod
+    def serialize(cls, obj: Any, **opts) -> str:
         return msgpack.packb(astuple(obj), **opts)
 
 
 class MsgPackDeserializer(Deserializer):
-    def deserialize(self, s, **opts):
+    @classmethod
+    def deserialize(cls, s, **opts):
         unp = msgpack.unpackb(s, raw=False, use_list=False, **opts)
         logger.debug('unpack from msgpack: {unp}')
         return unp

serde/se.py

@@ -27,7 +27,7 @@ class Serializer(metaclass=abc.ABCMeta):
     """
 
     @abc.abstractclassmethod
-    def serialize(self, obj):
+    def serialize(cls, obj):
         pass
 
 
@@ -72,7 +72,7 @@ def wrap(cls: Type[T]) -> Type[T]:
             setattr(cls, HIDDEN_NAME, Hidden())
 
         def serialize(self, ser, **opts) -> None:
-            return ser().serialize(self, **opts)
+            return ser.serialize(self, **opts)
 
         setattr(cls, SE_NAME, serialize)
         cls = se_func(cls, TO_ITER, render_astuple(cls))
@@ -185,10 +185,11 @@ class Field:
     case: Optional[str] = None
     rename: Optional[str] = None
     skip: Optional[bool] = None
+    skip_if_false: Optional[bool] = None
 
     @staticmethod
     def from_dataclass(f: DataclassField) -> '':
-        return Field(f.type, f.name, rename = f.metadata.get('serde_rename'), skip = f.metadata.get('serde_skip'))
+        return Field(f.type, f.name, rename = f.metadata.get('serde_rename'), skip = f.metadata.get('serde_skip'), skip_if_false = f.metadata.get('serde_skip_if_false'))
 
     @property
     def varname(self) -> str:
@@ -248,7 +249,12 @@ def {{func}}(obj):
   res = {}
   {% for f in cls|fields -%}
   {% if not f.skip|default(False) %}
+    {% if f.skip_if_false|default(False) %}
+  if {{f|arg|rvalue()}}:
+    res["{{f|case}}"] = {{f|arg|rvalue()}}
+    {% else %}
   res["{{f|case}}"] = {{f|arg|rvalue()}}
+    {% endif %}
   {% endif %}
   {% endfor -%}
   return res

serde/toml.py

@@ -9,16 +9,18 @@
 
 
 class TomlSerializer(Serializer):
-    def serialize(self, obj, **opts) -> str:
+    @classmethod
+    def serialize(cls, obj, **opts) -> str:
         return toml.dumps(asdict(obj))
 
 
 class TomlDeserializer(Deserializer):
-    def deserialize(self, s, **opts):
+    @classmethod
+    def deserialize(cls, s, **opts):
         return toml.loads(s)
 
 
-def to_toml(obj, se=TomlSerializer) -> str:
+def to_toml(obj, se: Type[TomlSerializer]=TomlSerializer) -> str:
     """
     Take an object and return toml string.
 
@@ -45,7 +47,7 @@ def to_toml(obj, se=TomlSerializer) -> str:
     if is_serializable(obj):
         return obj.__serde_serialize__(se)
     else:
-        return se().serialize(obj)
+        return se.serialize(obj)
 
 
 def from_toml(c: Type[T], s: str, de: Type[Deserializer] = TomlDeserializer) -> T:

serde/yaml.py

@@ -9,12 +9,14 @@
 
 
 class YamlSerializer(Serializer):
-    def serialize(self, obj, **opts) -> str:
+    @classmethod
+    def serialize(cls, obj, **opts) -> str:
         return yaml.safe_dump(asdict(obj), **opts)
 
 
 class YamlDeserializer(Deserializer):
-    def deserialize(self, s, **opts):
+    @classmethod
+    def deserialize(cls, s, **opts):
         return yaml.safe_load(s, **opts)
 
 
@@ -39,7 +41,7 @@ def to_yaml(obj, se: Type[Serializer] = YamlSerializer) -> str:
     if is_serializable(obj):
         return obj.__serde_serialize__(se)
     else:
-        return se().serialize(obj)
+        return se.serialize(obj)
 
 
 def from_yaml(c: Type[T], s: str, de: Type[Deserializer] = YamlDeserializer) -> T: