title: How to create a number of empty nested lists in python
body: <p>I want to have a variable that is a nested list of a number of empty lists that I can fill in later. Something that looks like:  </p>
  
  <pre><code>my_variable=[[], [], [], []]
  </code></pre>
  
  <p>However, I do not know beforehand how many lists I will need, only at the creation step, therefore I need a variable <code>a</code> to determine it. 
  I thought about simple <code>my_variable=[[]]*a</code>, but that creates copies of lists and it is not what I want to have. </p>
  
  <p>I could do:</p>
  
  <pre><code>my_variable=[]  
  for x in range(a):
     my_variable.append([])
  </code></pre>
  
  <p>but I'm looking for a more elegant solution (preferably one-liner). Is there any?</p>