title: Convert string to negative number
body: <p>I need to convert from string type to a number</p>
  
  <pre><code>list = ["-5","4","-3","variable"]  # Input
  
  list = [-5,4,-3,"variable"]        # epected output
  </code></pre>
  
  <p>I have a problem when converting the negative number</p>
  
  <pre><code>list[0]=int(list[0])
  </code></pre>
  
  <blockquote>
    <p>ValueError: invalid literal for int() with base 10: '-5'</p>
  </blockquote>