Implement get_callback that allows modifying returned value to the Field class

osc/util/models.py

@@ -10,6 +10,7 @@ import copy
 import inspect
 import sys
 import types
+from typing import Callable
 from typing import get_type_hints
 
 # supported types
@@ -76,6 +77,7 @@ class Field(property):
         default: Any = NotSet,
         description: Optional[str] = None,
         exclude: bool = False,
+        get_callback: Optional[Callable] = None,
         **extra,
     ):
         # the default value; it can be a factory function that is lazily evaluated on the first use
@@ -106,6 +108,10 @@ class Field(property):
         # whether to exclude this field from export
         self.exclude = exclude
 
+        # optional callback to postprocess returned field value
+        # it takes (model_instance, value) and returns modified value
+        self.get_callback = get_callback
+
         # extra fields
         self.extra = extra
 
@@ -235,12 +241,18 @@ class Field(property):
 
     def get(self, obj):
         try:
-            return obj._values[self.name]
+            result = obj._values[self.name]
+            if self.get_callback is not None:
+                result = self.get_callback(obj, result)
+            return result
         except KeyError:
             pass
 
         try:
-            return obj._defaults[self.name]
+            result = obj._defaults[self.name]
+            if self.get_callback is not None:
+                result = self.get_callback(obj, result)
+            return result
         except KeyError:
             pass
 

tests/test_models.py

@@ -291,6 +291,31 @@ class Test(unittest.TestCase):
         self.assertEqual(c.field, "new-text")
         self.assertEqual(c.field2, "text")
 
+    def test_get_callback(self):
+        class Model(BaseModel):
+            quiet: bool = Field(
+                default=False,
+            )
+            verbose: bool = Field(
+                default=False,
+                # return False if ``quiet`` is True; return the actual value otherwise
+                get_callback=lambda obj, value: False if obj.quiet else value,
+            )
+
+        m = Model()
+        self.assertEqual(m.quiet, False)
+        self.assertEqual(m.verbose, False)
+
+        m.quiet = True
+        m.verbose = True
+        self.assertEqual(m.quiet, True)
+        self.assertEqual(m.verbose, False)
+
+        m.quiet = False
+        m.verbose = True
+        self.assertEqual(m.quiet, False)
+        self.assertEqual(m.verbose, True)
+
 
 if __name__ == "__main__":
     unittest.main()