title: Regular expression: alphanumerics without pure numerics
body: <p>I need to extract the names of variables from a function string.</p>
  
  <p>A variable can be [a-zA-Z0-9]+ but <strong>not</strong> a real number notated like 1, 3.5, 1e4, 1e5...</p>
  
  <p>Is there a smart way of doing this?</p>
  
  <p>Here's a M(not)WE in python:</p>
  
  <pre><code>import re
  pattern = r"[a-zA-z0-9.]+"
  function_string = "(A+B1)**2.5"
  re.findall(pattern, function_string)
  </code></pre>
  
  <p>The above code returns:</p>
  
  <pre><code>A, B1 and 2.5.
  </code></pre>
  
  <p>My desired output is </p>
  
  <pre><code>A and B1.
  </code></pre>
  
  <p>And here's a nice way of testing the regular expressions:
  <a href="https://regex101.com/r/fv0DfR/1" rel="nofollow noreferrer">https://regex101.com/r/fv0DfR/1</a></p>