diff --git a/python/obitools3/utils.pxd b/python/obitools3/utils.pxd
index 3a6db25..4d9849d 100644
--- a/python/obitools3/utils.pxd
+++ b/python/obitools3/utils.pxd
@@ -12,4 +12,6 @@ cdef str tostr(object string)
 cdef obitype_t get_obitype_single_value(object value)
 cdef obitype_t update_obitype(obitype_t obitype, object new_value)
 cdef obitype_t get_obitype_iterable_value(object value)
-cdef obitype_t get_obitype(object value)
\ No newline at end of file
+cdef obitype_t get_obitype(object value)
+
+cdef object __etag__(str x)
diff --git a/python/obitools3/utils.pyx b/python/obitools3/utils.pyx
index acc884f..5d0bb83 100644
--- a/python/obitools3/utils.pyx
+++ b/python/obitools3/utils.pyx
@@ -15,6 +15,8 @@ from obitools3.dms.capi.obierrno cimport OBI_LINE_IDX_ERROR, \
                                          OBI_ELT_IDX_ERROR
                                          #obi_errno
 
+import re
+
 #from obitools3.dms.obiseq cimport Nuc_Seq, Nuc_Seq_Stored
 
 
@@ -156,3 +158,50 @@ cdef obitype_t get_obitype(object value) :
     
     else :
         return get_obitype_single_value(value)
+
+
+__re_int__      = re.compile("^[+-]?[0-9]+$")
+__re_float__    = re.compile("^[+-]?[0-9]+(\.[0-9]*)?([eE][+-]?[0-9]+)?$")
+__re_str__      = re.compile("""^"[^"]*"|'[^']*'$""")
+__re_dict__     = re.compile("""^\{\ *
+                                   (
+                                       ("[^"]*"|'[^']*')
+                                        \ *:\ *
+                                       ([^,}]+|
+                                        "[^"]*"|
+                                        '[^']*'
+                                       )
+                                   )?
+                                   (\ *,\ *
+                                       ("[^"]*"|'[^']*')
+                                        \ *:\ *
+                                       ([^,}]+|
+                                        "[^"]*"|
+                                        '[^']*'
+                                       )
+                                    )*\ *\}$""", re.VERBOSE)
+
+__re_val__ = re.compile("""(("[^"]*"|'[^']*') *: *([^,}]+|"[^"]*"|'[^']*') *[,}] *)""")
+
+cdef object __etag__(str x):
+    cdef list elements
+    cdef tuple i
+    
+    if __re_int__.match(x):
+        v=int(x)
+    elif __re_float__.match(x):
+        v=float(x)
+    elif __re_str__.match(x):
+        v=x[1:-1]
+    elif x=='None':
+        v=None
+    elif x=='False':
+        v=False
+    elif x=='True':
+        v=True
+    elif __re_dict__.match(x):
+        elements=__re_val__.findall(x)
+        v=dict([(i[1][1:-1],__etag__(i[2])) for i in elements])
+    else:
+        v=x
+    return v