Attributes from netCDF4 intialization retained

Ensures that attrs for open_mfdataset are now retained

xarray/core/merge.py

@@ -371,6 +371,42 @@ def _get_priority_vars(objects, priority_arg, compat='equals'):
         priority_vars = merge_variables(expanded, compat=compat)
     return priority_vars
 
+def _merge_attrs(objects, mergesep='; '):
+    """ Merge attrs from a list of objects
+
+    This is needed to merge multiple object all containing attributes.
+
+    Parameters
+    ----------
+    objects : list of objects containing attributes
+        Each item in list has an associated attrs
+    mergesep : str, optional
+        Merge separator for output of merged attribute strings
+
+    Returns
+    -------
+    Merged attributes from attr property of each item in objects
+
+    """
+
+    mergedattrs = OrderedDict()
+
+    # merge the attributes (ignoring order)
+    for attrs in [aobj.attrs for aobj in objects]:
+        for k, v in attrs.iteritems():
+            vals = mergedattrs.get(k, set())
+            vals.add(v)
+            mergedattrs[k] = vals
+
+    # format for output
+    for k, v in mergedattrs.iteritems():
+        if len(v) == 1:
+            mergedattrs[k] = v.pop()
+        else:
+            mergedattrs[k] = mergesep.join(list(v))
+
+    return mergedattrs
+
 
 def merge_coords(objs, compat='minimal', join='outer', priority_arg=None,
                  indexes=None):
@@ -532,7 +568,8 @@ def merge(objects, compat='no_conflicts', join='outer'):
                          for obj in objects]
 
     variables, coord_names, dims = merge_core(dict_like_objects, compat, join)
-    merged = Dataset._construct_direct(variables, coord_names, dims)
+    attrs = _merge_attrs(dict_like_objects)
+    merged = Dataset._construct_direct(variables, coord_names, dims, attrs)
 
     return merged