step 2 of fixing export from grids when there are virtual fields. Note export hidden columns includes all table fields and any virtual fields which are displayed, but it does not pick up virtual fields which are not displayed.

gluon/sqlhtml.py

@@ -2183,14 +2183,15 @@ class SQLFORM(FORM):
             expcolumns = [str(f) for f in columns]
             selectable_columns = [str(f) for f in columns if not isinstance(f,Field.Virtual)]
             if export_type.endswith('with_hidden_cols'):
-                expcolumns = []
+                #expcolumns = [] start with the visible columns, which includes visible virtual fields
                 selectable_columns=[]  #like expcolumns but excluding virtual
                 for table in tables:
                     for field in table:
-                        if field.readable and field.tablename in tablenames:
-                            expcolumns.append(field)
+                        if field.readable and field.tablename in tablenames:  #this does not find virtual fields
+                            if not str(field) in expcolumns:
+                                expcolumns.append(str(field))
                             if not(isinstance(field,Field.Virtual)):
-                                selectable_columns.append(field)
+                                selectable_columns.append(str(field))
 
             if export_type in exportManager and exportManager[export_type]:
                 if request.vars.keywords:
@@ -2212,6 +2213,7 @@ class SQLFORM(FORM):
 
                 value = exportManager[export_type]
                 clazz = value[0] if hasattr(value, '__getitem__') else value
+                rows.colnames = expcolumns # rows.colnames is selectable fields, it misses virtual fields
                 oExp = clazz(rows)
                 filename = '.'.join(('rows', oExp.file_ext))
                 response.headers['Content-Type'] = oExp.content_type