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.

rest_framework/fields.py

@@ -109,27 +109,6 @@ 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

@@ -26,7 +26,7 @@ from django.utils.translation import gettext_lazy as _
 
 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 (
@@ -337,6 +337,27 @@ class Serializer(BaseSerializer, metaclass=SerializerMetaclass):
         'invalid': _('Invalid data. Expected a dictionary, but got {datatype}.')
     }
 
+    @staticmethod
+    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
+
     @cached_property
     def fields(self):
         """
@@ -483,7 +504,7 @@ class Serializer(BaseSerializer, metaclass=SerializerMetaclass):
             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)