Removed redundancy in Graph API (#144)

pydatastructs/graphs/graph.py

@@ -12,7 +12,8 @@ class Graph(object):
 
     implementation: str
         The implementation to be used for storing
-        graph in memory.
+        graph in memory. It can be figured out
+        from type of the vertices(if passed at construction).
         By default, 'adjacency_list'.
     vertices: AdjacencyListGraphNode(s)
         For AdjacencyList implementation vertices
@@ -47,7 +48,8 @@ class Graph(object):
     __slots__ = ['_impl']
 
     def __new__(cls, *args, **kwargs):
-        implementation = kwargs.get('implementation', 'adjacency_list')
+        default_impl = args[0]._impl if args else 'adjacency_list'
+        implementation = kwargs.get('implementation', default_impl)
         if implementation is 'adjacency_list':
             from pydatastructs.graphs.adjacency_list import AdjacencyList
             obj = AdjacencyList(*args)

pydatastructs/utils/misc_util.py

@@ -153,6 +153,7 @@ class AdjacencyListGraphNode(GraphNode):
     def __new__(cls, name, data=None, adjacency_list=None):
         obj = GraphNode.__new__(cls)
         obj.name, obj.data = str(name), data
+        obj._impl = 'adjacency_list'
         if adjacency_list is not None:
             for node in adjacency_list:
                 obj.__setattr__(node.name, node)
@@ -201,6 +202,7 @@ def __new__(cls, name, data=None):
         obj = GraphNode.__new__(cls)
         obj.name, obj.data, obj.is_connected = \
             int(name), data, None
+        obj._impl = 'adjacency_matrix'
         return obj
 
 class GraphEdge(object):