title: Regex to extract ONLY alphanumeric words
body: <p>I am looking for a regex to extract the word that ONLY contain alphanumeic characters:</p>
  
  <pre><code>string = 'This is a $dollar sign !!'
  matches = re.findall(regex, string)
  matches = ['This', 'is', 'sign']
  </code></pre>
  
  <p>This can be done by tokenizing the string and evaluate each token individually using the following regex:</p>
  
  <pre><code>^[a-zA-Z0-9]+$
  </code></pre>
  
  <p>Due to performance issues, I want to able to extract the alphanumeric tokens without tokenizing the whole string. The closest I got to was</p>
  
  <pre><code>regex = \b[a-zA-Z0-9]+\b
  </code></pre>
  
  <p>, but it still extracts substrings containing alphanumeric characters:</p>
  
  <pre><code>string = 'This is a $dollar sign !!'
  matches = re.findall(regex, string)
  matches = ['This', 'is', 'dollar', 'sign']
  </code></pre>
  
  <p>Is there a regex able to pull this off? I've tried different things but can't come up with a solution.</p>