title: lambda explanation on the parameters used
body: <p>I would like to inquire about something rather simple which is about lambda parameters.</p>
  
  <p>I understand how the function of lambda works but when it comes to this I got confused with which is which parameters.</p>
  
  <p>Example:</p>
  
  <pre><code>from functools import reduce
  
  # Simple example so that I could understand based on the explanation from experts
  # here. You could modify as however you wish to explain it.
  product = reduce(lambda x, y: x + y, [1,2,3,4])
  </code></pre>
  
  <p>Here is a shorter version to compare it:</p>
  
  <pre><code>product = 0
  for x in [1,2,3,4]:
      product = product + x
  print(product)
  </code></pre>
  
  <p>Now, my question is <code>x</code> is the variable for the list or <code>y</code> is the variable for the list in the first example for lambda? And what is the default value for either <code>x</code> or <code>y</code> (judging either one of it belongs to product? since I did not initiate the initial value for it for the "lambda example" and only the second example I initialized.)</p>