title: Don't understand this python For loop
body: <p>I'm still a python newb, but I'm working through the <a href="http://pyneurgen.sourceforge.net/tutorial_nn.html" rel="noreferrer">Pyneurgen neural network tutorial</a>, and I don't fully understand how the for loop used to create the input data works in this instance:</p>
  
  <pre><code>for position, target in population_gen(population):
      pos = float(position)
      all_inputs.append([random.random(), pos * factor])
      all_targets.append([target])`
  </code></pre>
  
  <p>What is the loop iterating through exactly? I've not come across the use of the comma and a function in the loop before.</p>
  
  <p>Thanks in advance for any help :)</p>