Make set_value a method within Serializer (#8001)

* Make set_value a static method for Serializers

As an alternative to #7671, let the method be overridden if needed. As
the function is only used for serializers, it has a better place in the
Serializer class.

* Set `set_value` as an object (non-static) method

* Add tests for set_value()

These tests follow the examples given in the method.

rest_framework/fields.py

@@ -113,27 +113,6 @@ def get_attribute(instance, attrs):
     return instance
 
 
-def set_value(dictionary, keys, value):
-    """
-    Similar to Python's built in `dictionary[key] = value`,
-    but takes a list of nested keys instead of a single key.
-
-    set_value({'a': 1}, [], {'b': 2}) -> {'a': 1, 'b': 2}
-    set_value({'a': 1}, ['x'], 2) -> {'a': 1, 'x': 2}
-    set_value({'a': 1}, ['x', 'y'], 2) -> {'a': 1, 'x': {'y': 2}}
-    """
-    if not keys:
-        dictionary.update(value)
-        return
-
-    for key in keys[:-1]:
-        if key not in dictionary:
-            dictionary[key] = {}
-        dictionary = dictionary[key]
-
-    dictionary[keys[-1]] = value
-
-
 def to_choices_dict(choices):
     """
     Convert choices into key/value dicts.

rest_framework/serializers.py

@@ -28,7 +28,7 @@
 
 from rest_framework.compat import postgres_fields
 from rest_framework.exceptions import ErrorDetail, ValidationError
-from rest_framework.fields import get_error_detail, set_value
+from rest_framework.fields import get_error_detail
 from rest_framework.settings import api_settings
 from rest_framework.utils import html, model_meta, representation
 from rest_framework.utils.field_mapping import (
@@ -346,6 +346,26 @@ class Serializer(BaseSerializer, metaclass=SerializerMetaclass):
         'invalid': _('Invalid data. Expected a dictionary, but got {datatype}.')
     }
 
+    def set_value(self, dictionary, keys, value):
+        """
+        Similar to Python's built in `dictionary[key] = value`,
+        but takes a list of nested keys instead of a single key.
+
+        set_value({'a': 1}, [], {'b': 2}) -> {'a': 1, 'b': 2}
+        set_value({'a': 1}, ['x'], 2) -> {'a': 1, 'x': 2}
+        set_value({'a': 1}, ['x', 'y'], 2) -> {'a': 1, 'x': {'y': 2}}
+        """
+        if not keys:
+            dictionary.update(value)
+            return
+
+        for key in keys[:-1]:
+            if key not in dictionary:
+                dictionary[key] = {}
+            dictionary = dictionary[key]
+
+        dictionary[keys[-1]] = value
+
     @cached_property
     def fields(self):
         """
@@ -492,7 +512,7 @@ def to_internal_value(self, data):
             except SkipField:
                 pass
             else:
-                set_value(ret, field.source_attrs, validated_value)
+                self.set_value(ret, field.source_attrs, validated_value)
 
         if errors:
             raise ValidationError(errors)

tests/test_serializer.py

@@ -762,3 +762,24 @@ class TestSerializer(serializers.Serializer):
 
         assert (s.data | {}).__class__ == s.data.__class__
         assert ({} | s.data).__class__ == s.data.__class__
+
+
+class TestSetValueMethod:
+    # Serializer.set_value() modifies the first parameter in-place.
+
+    s = serializers.Serializer()
+
+    def test_no_keys(self):
+        ret = {'a': 1}
+        self.s.set_value(ret, [], {'b': 2})
+        assert ret == {'a': 1, 'b': 2}
+
+    def test_one_key(self):
+        ret = {'a': 1}
+        self.s.set_value(ret, ['x'], 2)
+        assert ret == {'a': 1, 'x': 2}
+
+    def test_nested_key(self):
+        ret = {'a': 1}
+        self.s.set_value(ret, ['x', 'y'], 2)
+        assert ret == {'a': 1, 'x': {'y': 2}}