Collect tracking ids and add them to mf_dset

tzis/tzis.py

@@ -34,6 +34,16 @@ class Tzis():
         #if type(mf) != list and type(mf) != str :
         #    raise ValueError("Dataset '{0}' must either be a string or a list of strings")
         if mf:
+            tracking_ids=[]
+            if type(mf) == str :
+                mf = [mf]
+            try :
+                for dset in mf :
+                    dset = xarray.open_dataset(dset)
+                    tracking_ids.append(dset.attrs["tracking_id"])
+            except :
+                if self.verbose :
+                    print("Could not collect 'tracking_ids'.")
             if xarray_kwargs:
                 mf_dset = xarray.open_mfdataset(mf,
                                  decode_cf=True,
@@ -51,6 +61,8 @@ class Tzis():
                                  data_vars='minimal', 
                                  coords='minimal', 
                                  compat='override')
+            if tracking_ids :
+                mf_dset.attrs["tracking_id"]=tracking_ids
 
             if not self.varname :
                 self.varname = mf_dset.variables[0]