Trac #19440: cluster seed is no longer hashable

With the recent change in the cluster code,
{{{
sage: Q= ClusterQuiver(['D',4])
sage: hash(Q)
Traceback (most recent call last):
...
TypeError: <class
'sage.combinat.cluster_algebra_quiver.quiver.ClusterQuiver'> is not
hashable
}}}
And this has very bad consequences !

URL: http://trac.sagemath.org/19440
Reported by: chapoton
Ticket author(s): Frédéric Chapoton
Reviewer(s): Christian Stump

Author: Release Manager

src/sage/combinat/cluster_algebra_quiver/cluster_seed.py

@@ -213,6 +213,7 @@ def __init__(self, data, frozen=None, is_principal=False, user_labels=None, user
 
             # Copy the following attributes from data
             self._M = copy( data._M )
+            self._M.set_immutable()
             self._B = copy( data._B )
             self._n = data._n
             self._m = data._m
@@ -269,6 +270,7 @@ def __init__(self, data, frozen=None, is_principal=False, user_labels=None, user
             quiver = ClusterQuiver( data )
 
             self._M = copy(quiver._M)    # B-tilde exchange matrix
+            self._M.set_immutable()
             self._n = quiver._n
             self._m = quiver._m
             self._B = copy(self._M[:self._n,:self._n])  # Square Part of the B_matrix
@@ -397,6 +399,7 @@ def use_c_vectors(self, use=True, bot_is_c=False, force=False):
                     self._C = copy(self._M[self._m:(self._n+self._m),:self._n])
                     self._BC = copy(self._M)
                     self._M = self._M[:self._m:self._n]
+                    self._M.set_immutable()
                     self._bot_is_c = False
 
     def use_g_vectors(self, use=True, force=False):
@@ -858,6 +861,27 @@ def __eq__(self, other):
             d_vec = self.d_matrix() == other.d_matrix()
         return g_vec and c_vec and d_vec and clusters and ExMat
 
+    def __hash__(self):
+        """
+        Return a hash of ``self``.
+
+        EXAMPLES::
+
+            sage: Q = ClusterSeed(['A',5])
+            sage: hash(Q)  # indirect doctest
+            -5649412990944896369  # 64-bit
+            222337679  # 32-bit
+        """
+        # mat_hash = self._M.__hash__()
+        if self._use_fpolys:
+            return tuple(self.cluster()).__hash__()
+        elif self._use_g_vec:
+            return self.g_matrix().__hash__()
+        elif self._use_c_vec:
+            return self.c_matrix().__hash__()
+        elif self._use_d_vec:
+            return self.d_matrix().__hash__()
+
     def _repr_(self):
         r"""
         Returns the description of ``self``.
@@ -1077,7 +1101,7 @@ def b_matrix(self):
             [ 0  0  0  1]
             [ 0  0 -2  0]
         """
-        return copy( self._M )
+        return copy(self._M)
 
     def ground_field(self):
         r"""
@@ -2359,6 +2383,7 @@ def mutate(self, sequence, inplace=True):
 
             seed._BC.mutate(k)
             seed._M = copy(seed._BC[:n+m,:n])
+            self._M.set_immutable()
 
             if seed._use_c_vec:
                 seed._C = seed._BC[n+m:2*n+m,:n+m]
@@ -3050,15 +3075,19 @@ def reset_coefficients( self ):
             [ 0  1  0]
             [ 0  0  1]
         """
-        n,m = self._n, self._m
+        n, m = self._n, self._m
         if not n == m:
-            raise ValueError("The numbers of cluster variables and of frozen variables do not coincide.")
+            raise ValueError("The numbers of cluster variables "
+                             "and of frozen variables do not coincide.")
+        newM = copy(self._M)
         for i in xrange(m):
             for j in xrange(n):
                 if i == j:
-                    self._M[i+n,j] = 1
+                    newM[i + n, j] = 1
                 else:
-                    self._M[i+n,j] = 0
+                    newM[i + n, j] = 0
+        self._M = newM
+        self._M.set_immutable()
         self._quiver = None
         self._is_principal = None
 

src/sage/combinat/cluster_algebra_quiver/quiver.py

@@ -265,6 +265,7 @@ def __init__( self, data, frozen=None ):
                 print 'The input data is a quiver, therefore the additional parameter frozen is ignored.'
 
             self._M = copy(data._M)
+            self._M.set_immutable()
             self._n = data._n
             self._m = data._m
             self._digraph = copy( data._digraph )
@@ -280,6 +281,7 @@ def __init__( self, data, frozen=None ):
                 print 'The input data is a matrix, therefore the additional parameter frozen is ignored.'
 
             self._M = copy(data).sparse_matrix()
+            self._M.set_immutable()
             self._n = n = self._M.ncols()
             self._m = m = self._M.nrows() - self._n
             self._digraph = _matrix_to_digraph( self._M )
@@ -344,6 +346,7 @@ def __init__( self, data, frozen=None ):
             self._digraph = dg
             self._vertex_dictionary = {}
             self._M = M
+            self._M.set_immutable()
             if n+m == 0:
                 self._description = 'Quiver without vertices'
             elif n+m == 1:
@@ -378,6 +381,18 @@ def __eq__(self, other):
         """
         return isinstance(other, ClusterQuiver) and self._M == other._M
 
+    def __hash__(self):
+        """
+        Return a hash of ``self``.
+
+        EXAMPLES::
+
+            sage: Q = ClusterQuiver(['A',5])
+            sage: hash(Q)  # indirect doctest
+            16
+        """
+        return self._M.__hash__()
+
     def _repr_(self):
         """
         Returns the description of ``self``.
@@ -715,7 +730,7 @@ def b_matrix(self):
             [ 0  0  0  1]
             [ 0  0 -2  0]
         """
-        return copy( self._M )
+        return copy(self._M)
 
     def digraph(self):
         """
@@ -1292,6 +1307,7 @@ def mutate(self, data, inplace=True):
         M = _edge_list_to_matrix( dg.edge_iterator(), n, m )
         if inplace:
             self._M = M
+            self._M.set_immutable()
             self._digraph = dg
         else:
             Q = ClusterQuiver( M )
@@ -1402,6 +1418,7 @@ def reorient( self, data ):
                     dg_new.add_edge( edge[1],edge[0],edge[2] )
             self._digraph = dg_new
             self._M = _edge_list_to_matrix( dg_new.edges(), self._n, self._m )
+            self._M.set_immutable()
             self._mutation_type = None
         elif all( type(edge) in [list,tuple] and len(edge)==2 for edge in data ):
             edges = self._digraph.edges(labels=False)
@@ -1411,6 +1428,7 @@ def reorient( self, data ):
                     self._digraph.delete_edge(edge[1],edge[0])
                     self._digraph.add_edge(edge[0],edge[1],label)
             self._M = _edge_list_to_matrix( self._digraph.edges(), self._n, self._m )
+            self._M.set_immutable()
             self._mutation_type = None
         else:
             raise ValueError('The order is no total order on the vertices of the quiver or a list of edges to be oriented.')