Check for redundant on SerializerMethodField

rest_framework/fields.py

@@ -178,7 +178,7 @@ class Field(object):
         # In order to enforce a consistent style, we error if a redundant
         # 'source' argument has been used. For example:
         # my_field = serializer.CharField(source='my_field')
-        assert self._kwargs.get('source') != field_name, (
+        assert self.source != field_name, (
             "It is redundant to specify `source='%s'` on field '%s' in "
             "serializer '%s', because it is the same as the field name. "
             "Remove the `source` keyword argument." %
@@ -883,17 +883,32 @@ class SerializerMethodField(Field):
         def get_extra_info(self, obj):
             return ...  # Calculate some data to return.
     """
-    def __init__(self, method_attr=None, **kwargs):
+    def __init__(self, method_name=None, **kwargs):
-        self.method_attr = method_attr
+        self.method_name = method_name
         kwargs['source'] = '*'
         kwargs['read_only'] = True
         super(SerializerMethodField, self).__init__(**kwargs)
 
+    def bind(self, field_name, parent):
+        # In order to enforce a consistent style, we error if a redundant
+        # 'method_name' argument has been used. For example:
+        # my_field = serializer.CharField(source='my_field')
+        default_method_name = 'get_{field_name}'.format(field_name=field_name)
+        assert self.method_name != default_method_name, (
+            "It is redundant to specify `%s` on SerializerMethodField '%s' in "
+            "serializer '%s', because it is the same as the default method name. "
+            "Remove the `method_name` argument." %
+            (self.method_name, field_name, parent.__class__.__name__)
+        )
+
+        # The method name should default to `get_{field_name}`.
+        if self.method_name is None:
+            self.method_name = default_method_name
+
+        super(SerializerMethodField, self).bind(field_name, parent)
+
     def to_representation(self, value):
-        method_attr = self.method_attr
+        method = getattr(self.parent, self.method_name)
-        if method_attr is None:
-            method_attr = 'get_{field_name}'.format(field_name=self.field_name)
-        method = getattr(self.parent, method_attr)
         return method(value)
 
 

tests/test_fields.py

@@ -710,3 +710,33 @@ class TestMultipleChoiceField(FieldValues):
             ('diesel', 'Diesel'),
         ]
     )
+
+
+# Tests for SerializerMethodField.
+# --------------------------------
+
+class TestSerializerMethodField:
+    def test_serializer_method_field(self):
+        class ExampleSerializer(serializers.Serializer):
+            example_field = serializers.SerializerMethodField()
+
+            def get_example_field(self, obj):
+                return 'ran get_example_field(%d)' % obj['example_field']
+
+        serializer = ExampleSerializer({'example_field': 123})
+        assert serializer.data == {
+            'example_field': 'ran get_example_field(123)'
+        }
+
+    def test_redundant_method_name(self):
+        class ExampleSerializer(serializers.Serializer):
+            example_field = serializers.SerializerMethodField('get_example_field')
+
+        with pytest.raises(AssertionError) as exc_info:
+            ExampleSerializer()
+        assert str(exc_info.value) == (
+            "It is redundant to specify `get_example_field` on "
+            "SerializerMethodField 'example_field' in serializer "
+            "'ExampleSerializer', because it is the same as the default "
+            "method name. Remove the `method_name` argument."
+        )