title: Converting a list with dashes into numbers
body: <p>I made a list from a CSV file. It looks like this:</p>
  
  <pre><code>['18', '29', '0'...'0', '-14', '9']
  </code></pre>
  
  <p>It had a text element in the beginning, which I popped. Now, Python doesn't work with the list elements as with proper numbers. Whenever I try to parse the elements into floats, for example, I get the error message:</p>
  
  <pre><code>ValueError: could not convert string to float: -
  </code></pre>
  
  <p>My code looks like this:</p>
  
  <pre><code>list2=[[float(column) for column in row] for row in list1]
  </code></pre>
  
  <p>Or this:</p>
  
  <pre><code>list2 = [map(float, x) for x in list1]
  </code></pre>
  
  <p>Both versions produce the same result. If I try a different data type, I get messages like:</p>
  
  <pre><code>ValueError: invalid literal for int() with base 10: '-'
  </code></pre>
  
  <p>Can anyone tell me how do I get Python to parse the dash into a number correctly?</p>