tf.Graph.as_default()

as_default(self)
Returns a context manager that makes this `Graph` the default graph.

This method should be used if you want to create multiple graphs in the same process. For convenience, a global default graph is
provided, and all ops will be added to this graph if you do not create a new graph explicitly. Use this method with the `with` keyword
to specify that ops created within the scope of a block should be added to this graph.

Tensorflow常用方法