Add skeleton of Variable

python/paddle/v2/framework/graph.py

 import paddle.v2.framework.core as core
 
+__all__ = ['Block', 'Variable', 'Program']
+
+
+class Variable(object):
+    def __init__(self, block, name=None, shape=None, dtype=None,
+                 lod_level=None):
+        self.block = block
+
+        if name is None:
+            name = Variable._unique_var_name_()
+        self.proto = self.block.proto.new_var(name)
+
+        if shape is not None:
+            self.proto.set_shape(shape)
+
+        if dtype is not None:
+            # TODO(yuyang18): Convert dtype from numpy.dtype
+            self.proto.set_data_type(dtype)
+
+        if lod_level is not None:
+            # TODO(yuyang18): set_lod_level is not defined.
+            self.proto.set_lod_level(lod_level)
+
+        self.block.vars[name] = self
+
+    # TODO(yuyang18): Get methods
+
+    @staticmethod
+    def _unique_var_name_():
+        uid = core.unique_integer()  # unique during whole process.
+        return "_generated_var_%d" % uid
+
 
 class Block(object):
     def __init__(self, program, idx):
@@ -16,6 +48,9 @@ class Block(object):
     def idx(self):
         return self.proto.id
 
+    def create_var(self, *args, **kwargs):
+        return Variable(self, *args, **kwargs)
+
 
 class Program(object):
     @classmethod