Move function to compat.

rest_framework/compat.py

@@ -495,3 +495,16 @@ except ImportError:
     oauth2_provider_forms = None
     oauth2_provider_scope = None
     oauth2_constants = None
+
+# Handle lazy strings
+from django.utils.functional import Promise
+
+if six.PY3:
+    def is_non_str_iterable(obj):
+        if (isinstance(obj, str) or
+            (isinstance(obj, Promise) and obj._delegate_text)):
+            return False
+        return hasattr(obj, '__iter__')
+else:
+    def is_non_str_iterable(obj):
+        return hasattr(obj, '__iter__')

rest_framework/fields.py

@@ -19,7 +19,6 @@ from django.db.models.fields import BLANK_CHOICE_DASH
 from django import forms
 from django.forms import widgets
 from django.utils.encoding import is_protected_type
-from django.utils.functional import Promise
 from django.utils.translation import ugettext_lazy as _
 from django.utils.datastructures import SortedDict
 
@@ -27,7 +26,7 @@ from rest_framework import ISO_8601
 from rest_framework.compat import timezone, parse_date, parse_datetime, parse_time
 from rest_framework.compat import BytesIO
 from rest_framework.compat import six
-from rest_framework.compat import smart_text, force_text
+from rest_framework.compat import smart_text, force_text, is_non_str_iterable
 from rest_framework.settings import api_settings
 
 
@@ -46,16 +45,6 @@ def is_simple_callable(obj):
     len_defaults = len(defaults) if defaults else 0
     return len_args <= len_defaults
 
-if six.PY3:
-    def is_non_str_iterable(obj):
-        if (isinstance(obj, str) or
-            (isinstance(obj, Promise) and obj._delegate_text)):
-            return False
-        return hasattr(obj, '__iter__')
-else:
-    def is_non_str_iterable(obj):
-        return hasattr(obj, '__iter__')
-
 def get_component(obj, attr_name):
     """
     Given an object, and an attribute name,