Allow service modules to prepare data

This is useful for any service where simple templating isn't good
enough.

Signed-off-by: Jim Easterbrook <jim@jim-easterbrook.me.uk>

src/pywws/__init__.py

@@ -1,3 +1,3 @@
 __version__ = '18.5.0'
-_release = '1528'
-_commit = '10bccbf'
+_release = '1529'
+_commit = 'e5e311b'

src/pywws/service/__init__.py

@@ -133,8 +133,9 @@ def __init__(self, context):
                 'obsolete item "template" found in weather.ini '
                 'section [{}]'.format(self.service_name))
         # create templater
-        self.templater = pywws.template.Template(context, use_locale=False)
-        self.template_file = StringIO(self.template)
+        if self.template:
+            self.templater = pywws.template.Template(context, use_locale=False)
+            self.template_file = StringIO(self.template)
         # set timestamp of first data to upload
         earliest = self.context.calib_data.before(datetime.max) - max(
             timedelta(days=self.catchup), self.interval)
@@ -161,10 +162,7 @@ def upload(self, catchup=True, live_data=None, test_mode=False):
             timestamp = data['idx']
             if test_mode:
                 timestamp = None
-            # convert data
-            data_str = self.templater.make_text(self.template_file, data)
-            self.template_file.seek(0)
-            prepared_data = eval('{' + data_str + '}')
+            prepared_data = self.prepare_data(data)
             prepared_data.update(self.fixed_data)
             self.upload_thread.queue.append(
                 (timestamp, {'prepared_data': prepared_data, 'live': live}))
@@ -173,6 +171,11 @@ def upload(self, catchup=True, live_data=None, test_mode=False):
         if self.upload_thread.queue and not self.upload_thread.is_alive():
             self.upload_thread.start()
 
+    def prepare_data(self, data):
+        data_str = self.templater.make_text(self.template_file, data)
+        self.template_file.seek(0)
+        return eval('{' + data_str + '}')
+
     def next_data(self, catchup, live_data):
         if catchup:
             start = self.next_update