[fix] convert json engine result attributes to string - closes #1006

searx/engines/json_engine.py

 from json import loads
 from sys import version_info
 from searx.url_utils import urlencode
+from searx.utils import to_string
 
 if version_info[0] == 3:
     unicode = str
                 content = query(result, content_query)[0]
             except:
                 content = ""
-            results.append({'url': url, 'title': title, 'content': content})
+            results.append({
+                'url': to_string(url),
+                'title': to_string(title),
+                'content': to_string(content),
+            })
     else:
         for url, title, content in zip(
             query(json, url_query),
             query(json, title_query),
             query(json, content_query)
         ):
-            results.append({'url': url, 'title': title, 'content': content})
+            results.append({
+                'url': to_string(url),
+                'title': to_string(title),
+                'content': to_string(content),
+            })
 
     if not suggestion_query:
         return results

searx/utils.py

 from babel.dates import format_date
 from codecs import getincrementalencoder
 from imp import load_source
+from numbers import Number
 from os.path import splitext, join
 from random import choice
 import sys
         return hmac.new(bytes(secret_key), url, hashlib.sha256).hexdigest()
     else:
         return hmac.new(bytes(secret_key, 'utf-8'), url, hashlib.sha256).hexdigest()
+
+
+def to_string(obj):
+    if isinstance(obj, basestring):
+        return obj
+    if isinstance(obj, Number):
+        return unicode(obj)
+    if hasattr(obj, '__str__'):
+        return obj.__str__()
+    if hasattr(obj, '__repr__'):
+        return obj.__repr__()