title: Python - Ensuring a variable holds a positive number
body: <p>I am looking for an elegant way to ensure that a given variable remains positive.</p>
  
  <p>I have two variables that hold positive float numbers and I decrement them according to certain conditions. At the end I want to guarantee that I still have positive numbers (or 0 at most). The pseudo code looks something like this:</p>
  
  <pre><code>list = [...]
  
  value1 = N
  value2 = M
  
  for element in list:
      if ... :
          value1 -= X
      if ... :
          value2 -= Y
  </code></pre>
  
  <p>Is there a more elegant solution than just adding two <code>ifs</code> at the end?</p>