title: Python: Regular expression to match alpha-numeric not working?
body: <p>I am looking to match a string that is inputted from a website to check if is alpha-numeric and possibly contains an underscore.
  My code:</p>
  
  <pre><code>if re.match('[a-zA-Z0-9_]',playerName):
              # do stuff
  </code></pre>
  
  <p>For some reason, this matches with crazy chars for example: nIg○▲ ☆ ★ ◇ ◆</p>
  
  <p>I only want regular A-Z and 0-9 and _ matching, is there something i am missing here?</p>