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  3. Introduction to Network Analysis in Python

Exercise

Checking whether there are self-loops in the graph

As Eric discussed, NetworkX also allows edges that begin and end on the same node; while this would be non-intuitive for a social network graph, it is useful to model data such as trip networks, in which individuals begin at one location and end in another.

It is useful to check for this before proceeding with further analyses, and NetworkX graphs provide a method for this purpose: .number_of_selfloops().

In this exercise as well as later ones, you'll find the assert statement useful. An assert-ions checks whether the statement placed after it evaluates to True, otherwise it will throw an AssertionError.

To begin, use the .number_of_selfloops() method on T in the IPython Shell to get the number of edges that begin and end on the same node. A number of self-loops have been synthetically added to the graph. Your job in this exercise is to write a function that returns these edges.

Instructions

100 XP
  • Define a function called find_selfloop_nodes() which takes one argument: G.
    • Using a for loop, iterate over all the edges in G (excluding the metadata).
    • If node u is equal to node v:
      • Append u to the list nodes_in_selfloops.
      • Return the list nodes_in_selfloops.
  • Check that the number of self loops in the graph equals the number of nodes in self loops. This has been done for you, so hit 'Submit Answer' to see the result!