Fix choices in ChoiceField to support IntEnum

Python support Enum in version 3.4, but changed __str__ to int.__str__ until version 3.11 to better support the replacement of existing constants use-case.
[https://docs.python.org/3/library/enum.html#enum.IntEnum](https://docs.python.org/3/library/enum.html#enum.IntEnum)

rest_frame work support Python 3.6+, this commit will support the Enum in choices of Field.

rest_framework/fields.py

@@ -8,6 +8,7 @@
 import uuid
 from collections import OrderedDict
 from collections.abc import Mapping
+from enum import Enum
 
 from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
@@ -1397,7 +1398,8 @@ def __init__(self, choices, **kwargs):
     def to_internal_value(self, data):
         if data == '' and self.allow_blank:
             return ''
-
+        if isinstance(data, Enum) and str(data) != str(data.value):
+            data = data.value
         try:
             return self.choice_strings_to_values[str(data)]
         except KeyError:
@@ -1406,6 +1408,8 @@ def to_internal_value(self, data):
     def to_representation(self, value):
         if value in ('', None):
             return value
+        if isinstance(value, Enum) and str(value) != str(value.value):
+            value = value.value
         return self.choice_strings_to_values.get(str(value), value)
 
     def iter_options(self):
@@ -1429,7 +1433,7 @@ def _set_choices(self, choices):
         # Allows us to deal with eg. integer choices while supporting either
         # integer or string input, but still get the correct datatype out.
         self.choice_strings_to_values = {
-            str(key): key for key in self.choices
+            str(key.value) if isinstance(key, Enum) and str(key) != str(key.value) else str(key): key for key in self.choices
         }
 
     choices = property(_get_choices, _set_choices)
@@ -1815,6 +1819,7 @@ class HiddenField(Field):
     constraint on a pair of fields, as we need some way to include the date in
     the validated data.
     """
+
     def __init__(self, **kwargs):
         assert 'default' in kwargs, 'default is a required argument.'
         kwargs['write_only'] = True
@@ -1844,6 +1849,7 @@ class ExampleSerializer(Serializer):
         def get_extra_info(self, obj):
             return ...  # Calculate some data to return.
     """
+
     def __init__(self, method_name=None, **kwargs):
         self.method_name = method_name
         kwargs['source'] = '*'

tests/test_fields.py

@@ -131,6 +131,7 @@ class TestEmpty:
     """
     Tests for `required`, `allow_null`, `allow_blank`, `default`.
     """
+
     def test_required(self):
         """
         By default a field must be included in the input.
@@ -657,6 +658,7 @@ class FieldValues:
     """
     Base class for testing valid and invalid input values.
     """
+
     def test_valid_inputs(self, *args):
         """
         Ensure that valid values return the expected validated data.
@@ -1824,6 +1826,31 @@ def test_edit_choices(self):
             field.run_validation(2)
         assert exc_info.value.detail == ['"2" is not a valid choice.']
 
+    def test_enum_choices(self):
+        from enum import IntEnum, auto
+
+        class ChoiceCase(IntEnum):
+            first = auto()
+            second = auto()
+        # Enum validate
+        choices = [
+            (ChoiceCase.first, "1"),
+            (ChoiceCase.second, "2")
+        ]
+        field = serializers.ChoiceField(choices=choices)
+        assert field.run_validation(1) == 1
+        assert field.run_validation(ChoiceCase.first) == 1
+        assert field.run_validation("1") == 1
+        # Enum.value validate
+        choices = [
+            (ChoiceCase.first.value, "1"),
+            (ChoiceCase.second.value, "2")
+        ]
+        field = serializers.ChoiceField(choices=choices)
+        assert field.run_validation(1) == 1
+        assert field.run_validation(ChoiceCase.first) == 1
+        assert field.run_validation("1") == 1
+
 
 class TestChoiceFieldWithType(FieldValues):
     """