title: Regex as if string is a variable
body: <p>I'm working with a script that would determine if my string would be a valid variable.
  It's very basic but I can`t seem to figure out how to use regular expression.</p>
  
  <p>So basically I want:</p>
  
  <pre><code>A-Z
  a-z
  0-9
  no whitespace anywhere
  no special char except _
  </code></pre>
  
  <p>Is that possible ? 
  This is what I tried:</p>
  
  <pre><code>re.match("[a-zA-Z0-9_,/S]*$", char_s):
  </code></pre>