changed init of MrData to an empty list so data can be appended directly

da/ct/obs.py

@@ -81,7 +81,7 @@ class CtObservations(object):
     def __init__(self,DaSystem,sampledate):
 
         sfname      = DaSystem.da_settings['obs.input.fname']+'.%s'%(sampledate.strftime('%Y%m%d'),)+'.nc'
-        msg         = 'This filename is hardcoded but needs replacement' ; logging.warning(msg)
+        #msg         = 'This filename is hardcoded but needs replacement' ; logging.warning(msg)
         filename    = os.path.join(DaSystem.da_settings['obs.input.dir'],sfname)
 
         if not os.path.exists(filename):
@@ -90,7 +90,7 @@ class CtObservations(object):
         else:
             self.ObsFilename = filename
 
-        self.MrData = None
+        self.MrData = MixingRatioList([])
 
     def __str__(self):
         """ Prints a list of MixingRatioSample objects"""