title: python math.log(1/2) domain error
body: <p>I have a weird problem with python's math library's log function</p>
  
  <pre><code>&gt;&gt; math.log(1/2)
  Traceback (most recent call last):
    File "&lt;input&gt;", line 1, in &lt;module&gt;
  ValueError: math domain error
  
  &gt;&gt; math.log(0.5)
  -0.6931471805599453
  </code></pre>
  
  <p>Why is this happening? 
  My python version is 2.7.9</p>