docstr: Creates a Graph instance from the filename.
docstr_tok: ["Creates","a","Graph","instance","from","the","filename","."]
code: def create_graph(filename):
      """Creates a Graph instance from the filename."""
  
      # The file is assumed to be in the format from the VF2 graph database.
      # Each file is composed of 16-bit numbers (unsigned short int).
      # So we will want to read 2 bytes at a time.
  
      # We can read the number as follows:
      #   number = struct.unpack('<H', file.read(2))
      # This says, expect the data in little-endian encoding
      # as an unsigned short int and unpack 2 bytes from the file.
  
      fh = open(filename, mode="rb")
  
      # Grab the number of nodes.
      # Node numeration is 0-based, so the first node has index 0.
      nodes = struct.unpack("<H", fh.read(2))[0]
  
      graph = nx.Graph()
      for from_node in range(nodes):
          # Get the number of edges.
          edges = struct.unpack("<H", fh.read(2))[0]
          for edge in range(edges):
              # Get the terminal node.
              to_node = struct.unpack("<H", fh.read(2))[0]
              graph.add_edge(from_node, to_node)
  
      fh.close()
      return graph
  
imports: import importlib.resources
  import os
  import random
  import struct
  import networkx
  from networkx.algorithms import isomorphism
label_desc: Use image node_id 1 for calling the TestVF2GraphDB obj's underlying member method code with example usage: obj.create_graph(filename) and returns: graph