diff --git a/python/obitools3/obidms/_obidms.pyx b/python/obitools3/obidms/_obidms.pyx
index 46a39a9..c9c72a9 100644
--- a/python/obitools3/obidms/_obidms.pyx
+++ b/python/obitools3/obidms/_obidms.pyx
@@ -274,7 +274,15 @@ cdef class OBIDMS_column :
                 self.pointer = obi_clone_column(self.dms.pointer, column_name_b, version_number, clone_data)
             else :
                 self.pointer = obi_open_column(self.dms.pointer, column_name_b, version_number)
-        
+
+
+    def __len__(self):
+        return self.pointer.header.lines_used
+    
+    
+    def __sizeof__(self):
+        return (self.pointer.header.header_size + self.pointer.header.data_size)
+    
     
     def __iter__(self):
     
diff --git a/python/obitools3/obidms/capi/obidmscolumn.pxd b/python/obitools3/obidms/capi/obidmscolumn.pxd
index 71bbab0..44163dd 100644
--- a/python/obitools3/obidms/capi/obidmscolumn.pxd
+++ b/python/obitools3/obidms/capi/obidmscolumn.pxd
@@ -16,7 +16,8 @@ cdef extern from "obidmscolumn.h" nogil:
     
     struct OBIDMS_column_header_t:
         bint            little_endian
-        int             header_size
+        size_t          header_size
+        size_t          data_size
         index_t         line_count
         index_t         lines_used
         index_t         nb_elements_per_line