Explicitly convert Content-Length to string

mwclient/http.py

@@ -84,9 +84,9 @@ class HTTPPersistentConnection(object):
 			headers['Cookie'] = self.cookies[host].get_cookie_header()
 		if issubclass(data.__class__, upload.Upload):
 			headers['Content-Type'] = data.content_type
-			headers['Content-Length'] = data.length;
+			headers['Content-Length'] = str(data.length)
 		elif data:
-			headers['Content-Length'] = len(data)
+			headers['Content-Length'] = str(len(data))
 			
 		if _headers: headers.update(_headers)