title: Numpy: ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
body: <p>I've been trying to use numpy on Python to plot some data. However I'm getting an error I don't understand:</p>
  
  <blockquote>
    <p>ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()</p>
  </blockquote>
  
  <p>And this is the line supposed to cause the error (the third line):</p>
  
  <pre><code>def T(z):
  for i in range(3):
      if (z &lt;= z_tbl[i+1]):
          return T0_tbl[i]+a_tbl[i]*(z-z_tbl[i])
  return 0
  </code></pre>
  
  <p>Those lists are just some lists of integers, and z is an integer too</p>
  
  <p>How can i fix it?</p>