title: Get a sub-graph from one node in NetworkX
body: <h1>Context</h1>
  
  <p>This is the first time I have to work with <em>NetworkX</em> so either I can't read correctly the documentation, or I simply do not use the right vocabulary.</p>
  
  <h1>Problem</h1>
  
  <p>I am working with a <a href="https://networkx.github.io/documentation/stable/reference/classes/digraph.html" rel="noreferrer">DiGraph</a>, and I want to get a list of every nodes accessible starting from a specified node.</p>
  
  <p>I thought of making a sub-graph containing the nodes I just described, and I would siply have to iterate over that specific sub-graph. Unfortunately, I didn't find a way to create automatically a sub-graph with the condition I mentioned.</p>
  
  <p>It feels like an obvious feature. What am I missing ?</p>