se adiciona extensions para la dian

FossilOrigin-Name: f5521ddbfb903915de88a26ba5197b67efa1ebfd66337061ee9e3653c59dd217

facho/model/fields/virtual.py

@@ -0,0 +1,45 @@
+from .field import Field
+
+# Un campo virtual
+# no participa del renderizado
+# pero puede interactura con este
+class Virtual(Field):
+    def __init__(self,
+                 setter=None,
+                 getter='bob',
+                 default=None,
+                 update_internal=False):
+        self.default = default
+        self.setter = setter
+        self.getter = getter
+        self.values = {}
+        self.update_internal = update_internal
+        self.virtual = True
+
+    def __get__(self, inst, cls):
+        if inst is None:
+            return self
+        assert self.name is not None
+
+        value = self.default
+        try:
+            value = self.values[inst]
+        except KeyError:
+            pass
+
+        try:
+            self.values[inst] = getattr(inst, self.getter)(self.name, value)
+        except AttributeError:
+            self.values[inst] = value
+
+        return self.values[inst]
+    
+    def __set__(self, inst, value):
+        if self.update_internal:
+            inst._value = value
+
+        if self.setter is None:
+            self.values[inst] = value
+        else:
+            self.values[inst] = self._call(inst, self.setter, self.name, value)
+        self._changed_field(inst, self.name, value)