Replace type('') with six.text_type (#6482)

As all source files import unicode_literals, type('') is always
equivalent to six.text_type (str on Python 3 and unicode on Python 2).
Removes the need to call type(), is more explicit, and will be easier to
catch places to change for when it is time to eventually drop Python 2.

rest_framework/fields.py

@@ -1486,7 +1486,7 @@ class MultipleChoiceField(ChoiceField):
         return dictionary.get(self.field_name, empty)
 
     def to_internal_value(self, data):
-        if isinstance(data, type('')) or not hasattr(data, '__iter__'):
+        if isinstance(data, six.text_type) or not hasattr(data, '__iter__'):
             self.fail('not_a_list', input_type=type(data).__name__)
         if not self.allow_empty and len(data) == 0:
             self.fail('empty')
@@ -1660,7 +1660,7 @@ class ListField(Field):
         """
         if html.is_html_input(data):
             data = html.parse_html_list(data, default=[])
-        if isinstance(data, (type(''), Mapping)) or not hasattr(data, '__iter__'):
+        if isinstance(data, (six.text_type, Mapping)) or not hasattr(data, '__iter__'):
             self.fail('not_a_list', input_type=type(data).__name__)
         if not self.allow_empty and len(data) == 0:
             self.fail('empty')

rest_framework/relations.py

@@ -518,7 +518,7 @@ class ManyRelatedField(Field):
         return dictionary.get(self.field_name, empty)
 
     def to_internal_value(self, data):
-        if isinstance(data, type('')) or not hasattr(data, '__iter__'):
+        if isinstance(data, six.text_type) or not hasattr(data, '__iter__'):
             self.fail('not_a_list', input_type=type(data).__name__)
         if not self.allow_empty and len(data) == 0:
             self.fail('empty')

tests/test_pagination.py

@@ -5,6 +5,7 @@ import pytest
 from django.core.paginator import Paginator as DjangoPaginator
 from django.db import models
 from django.test import TestCase
+from django.utils import six
 
 from rest_framework import (
     exceptions, filters, generics, pagination, serializers, status
@@ -207,7 +208,7 @@ class TestPageNumberPagination:
             ]
         }
         assert self.pagination.display_page_controls
-        assert isinstance(self.pagination.to_html(), type(''))
+        assert isinstance(self.pagination.to_html(), six.text_type)
 
     def test_second_page(self):
         request = Request(factory.get('/', {'page': 2}))
@@ -313,7 +314,7 @@ class TestPageNumberPaginationOverride:
             ]
         }
         assert not self.pagination.display_page_controls
-        assert isinstance(self.pagination.to_html(), type(''))
+        assert isinstance(self.pagination.to_html(), six.text_type)
 
     def test_invalid_page(self):
         request = Request(factory.get('/', {'page': 'invalid'}))
@@ -368,7 +369,7 @@ class TestLimitOffset:
             ]
         }
         assert self.pagination.display_page_controls
-        assert isinstance(self.pagination.to_html(), type(''))
+        assert isinstance(self.pagination.to_html(), six.text_type)
 
     def test_pagination_not_applied_if_limit_or_default_limit_not_set(self):
         class MockPagination(pagination.LimitOffsetPagination):
@@ -631,7 +632,7 @@ class CursorPaginationTestsMixin:
         assert current == [1, 1, 1, 1, 1]
         assert next == [1, 2, 3, 4, 4]
 
-        assert isinstance(self.pagination.to_html(), type(''))
+        assert isinstance(self.pagination.to_html(), six.text_type)
 
     def test_cursor_pagination_with_page_size(self):
         (previous, current, next, previous_url, next_url) = self.get_pages('/?page_size=20')

tests/test_validation.py

@@ -5,6 +5,7 @@ import re
 from django.core.validators import MaxValueValidator, RegexValidator
 from django.db import models
 from django.test import TestCase
+from django.utils import six
 
 from rest_framework import generics, serializers, status
 from rest_framework.test import APIRequestFactory
@@ -111,7 +112,7 @@ class TestAvoidValidation(TestCase):
         assert not serializer.is_valid()
         assert serializer.errors == {
             'non_field_errors': [
-                'Invalid data. Expected a dictionary, but got %s.' % type('').__name__
+                'Invalid data. Expected a dictionary, but got %s.' % six.text_type.__name__
             ]
         }