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.

Author: jdufresne

rest_framework/fields.py

@@ -1486,7 +1486,7 @@ def get_value(self, dictionary):
         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 @@ def to_internal_value(self, data):
         """
         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 @@ def get_value(self, dictionary):
         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 @@
 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 @@ def test_no_page_number(self):
             ]
         }
         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 @@ def test_no_page_number(self):
             ]
         }
         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 @@ def test_no_offset(self):
             ]
         }
         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 @@ def test_cursor_pagination(self):
         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 @@
 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 @@ def test_serializer_errors_has_only_invalid_data_error(self):
         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__
             ]
         }