title: What is an expression like `[variable_name]` called and how is it used?
body: <p>I have been working through a <a href="https://github.com/tsoding/kdtree-in-python" rel="nofollow noreferrer">tutorial</a> and encountered unfamiliar Python syntax. Looking to identify what it's called and learn how it works.</p>
  
  <p><strong>Mystery Code</strong></p>
  
  <p>The <a href="https://github.com/tsoding/kdtree-in-python/blob/d4c4d2a15693b73ab5c3feeaf25bda75174faa5f/main.py#L162" rel="nofollow noreferrer">line(s) in question</a> involve a variable name surrounded by square braces before being set:</p>
  
  <pre><code>[pivot] = get_point_by_id(svg_tree, 'pivot')
  </code></pre>
  
  <p><strong>Relevant Clue to Posted Answers</strong></p>
  
  <p>My initial thought was that it had something to do with being set to a list since the return value from <a href="https://github.com/tsoding/kdtree-in-python/blob/d4c4d2a15693b73ab5c3feeaf25bda75174faa5f/main.py#L28" rel="nofollow noreferrer">get_point_by_id</a> is a list.</p>
  
  <p>Untouched, the code runs fine. But if I try to recreate the syntax like this:</p>
  
  <pre><code>[variable_name] = [1,2,3]
  print(variable_name)
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>ValueError: too many values to unpack (expected 1)
  </code></pre>