Cython API: in taxonomy, added get_taxon_at_rank() function for Taxonomy

class and rank_idx property for Taxon class

python/obitools3/dms/taxo/taxo.pxd

@@ -23,6 +23,7 @@ cdef class Taxonomy(OBIWrapper) :
     cpdef object get_family(self, int taxid)
     cpdef bytes get_scientific_name(self, int taxid)
     cpdef bytes get_rank(self, int taxid)
+    cpdef object get_taxon_at_rank(self, int taxid, object rank)
 
 
 cdef class Taxon :

python/obitools3/dms/taxo/taxo.pyx

@@ -159,6 +159,15 @@ cdef class Taxonomy(OBIWrapper) :
         return self._ranks[taxon_p.rank]
 
 
+    cpdef object get_taxon_at_rank(self, int taxid, object rank):
+        if isinstance(rank, str) or isinstance(rank, bytes):
+            rank = self._ranks.index(tobytes(rank))
+        try:
+            return [x.taxid for x in self.parental_tree_iterator(taxid) if x.rank_idx==rank][0]
+        except IndexError:
+            return None
+
+    
     def __len__(self):
         return self.pointer().taxa.count
 
@@ -272,7 +281,7 @@ cdef class Taxon :    # TODO dict subclass?
     def __richcmp__(self, Taxon taxon2, int op):
         return (self.name == taxon2.name) and \
                (self.taxid == taxon2.taxid) and \
-               (self.rank == taxon2.rank) and \
+               (self.rank_idx == taxon2.rank_idx) and \
                (self.farest == taxon2.farest) and \
                (self.parent.taxid == taxon2.parent.taxid) and \
                (self.preferred_name == taxon2.preferred_name)
@@ -293,6 +302,11 @@ cdef class Taxon :    # TODO dict subclass?
     def rank(self):
         return ((self._tax)._ranks)[(self._pointer).rank]
 
+    # rank_idx property getter
+    @property
+    def rank_idx(self):
+        return (self._pointer).rank
+
     # farest property getter
     @property
     def farest(self):
@@ -321,6 +335,7 @@ cdef class Taxon :    # TODO dict subclass?
         d['taxid']          = self.taxid
         d['name']           = self.name
         d['rank']           = self.rank
+        d['rank_idx']       = self.rank_idx
         d['preferred name'] = self.preferred_name
         d['parent']         = self.parent.taxid
         d['farest']         = self.farest