[autoparallel] added sharding spec conversion for linear handler (#1687)

colossalai/tensor/sharding_spec.py

@@ -6,6 +6,8 @@ from enum import Enum
 from functools import reduce
 import operator
 
+__all__ = ['_DimSpec', 'ShardingException', 'ShardingSpec']
+
 ALLGATHER_COST = 20
 SHARD_COST = 5
 STEP_PENALTY = 6
@@ -136,6 +138,10 @@ class _DimSpec:
         return difference
 
 
+class ShardingException(Exception):
+    pass
+
+
 class ShardingSpec:
     '''
     Sharding spec for a tensor, it contains info of the logical device mesh this tensor belong