Add NaturalSortField support.

savepointradio/radio/fields.py

@@ -0,0 +1,35 @@
+import re
+from unicodedata import normalize
+
+from django.db import models
+
+
+class NaturalSortField(models.CharField):
+    """
+    A custom model field specifically for storing a normalized unicode string,
+    with removed starting articles, for use in natural sorting.
+
+    Code is a modified version of 'django-naturalsortfield' by Nathan Reynolds:
+    https://github.com/nathforge/django-naturalsortfield
+    """
+    def __init__(self, for_field, **kwargs):
+        self.for_field = for_field
+        kwargs.setdefault('db_index', True)
+        kwargs.setdefault('editable', False)
+        kwargs.setdefault('max_length', 255)
+        super(NaturalSortField, self).__init__(**kwargs)
+
+    def pre_save(self, model_instance, add):
+        return self.naturalize(getattr(model_instance, self.for_field))
+
+    def naturalize(self, string):
+        def naturalize_int_match(match):
+            return '%08d' % (int(match.group(0)),)
+
+        string = normalize('NFKD', string).encode('ascii', 'ignore').decode('ascii')
+        string = string.lower()
+        string = string.strip()
+        string = re.sub(r'^(a|an|the)\s+', '', string)
+        string = re.sub(r'\d+', naturalize_int_match, string)
+
+        return string