title: Python - Evaluate math expression within string
body: <p>I have a question concerning evaluation of math expression within a string.
  For example my string is following:</p>
  
  <pre><code>my_str='I have 6 * (2 + 3) apples'
  </code></pre>
  
  <p>I am wondering how to evaluate this string and get the following result:</p>
  
  <pre><code>'I have 30 apples'
  </code></pre>
  
  <p>Is the any way to do this?</p>
  
  <p>Thanks in advance.</p>
  
  <p>P.S. python's <code>eval</code> function does not help in this case.  It raised an error, when trying to evaluate with the <code>eval</code> function.</p>