sage.combinat: Modularization fixes for imports

Author: Matthias Koeppe

src/sage/combinat/cluster_algebra_quiver/cluster_seed.py

@@ -44,10 +44,10 @@
 from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
 from sage.rings.fraction_field_element import FractionFieldElement
 from sage.sets.set import Set
-from sage.graphs.digraph import DiGraph
 from sage.combinat.cluster_algebra_quiver.quiver_mutation_type import QuiverMutationType_Irreducible, QuiverMutationType_Reducible
 from sage.combinat.cluster_algebra_quiver.mutation_type import is_mutation_finite
 from random import randint
+from sage.misc.lazy_import import lazy_import
 from sage.misc.misc_c import prod
 from sage.matrix.special import identity_matrix
 from sage.matrix.constructor import matrix
@@ -57,6 +57,8 @@
 
 from sage.combinat.cluster_algebra_quiver.interact import cluster_interact
 
+lazy_import('sage.graphs.digraph', 'DiGraph')
+
 
 class ClusterSeed(SageObject):
     r"""