human
Give me a the Python program you requested given the following:
I am working on the file "18-05-28-Complete-Guide-to-Tensorflow-for-Deep-Learning-with-Python/01-Introduction-to-Neural-Networks/01_Neural Network From Scratch.ipynb".
The first task is:
Graph
Can you write Python program for it?
assistant
#Here is the Python program you requested.

class Graph():  
    def __init__(self):
        self.operations = []
        self.placeholders = []
        self.variables = []
        
    def set_as_default(self):
        """
        Sets this Graph instance as the Global Default Graph
        """
        global _default_graph
        _default_graph = self