title: Python3 Numpy np.where Error
body: <p>I have 2 lists like these</p>
  
  <pre><code>x = [None,[1, 15, 175, 20],
      [150, 175, 18, 20],
      [150, 175, 18],
      [192, 150, 177],...]
  
  
  y = [None,[12, 43, 55, 231],
      [243, 334, 44, 12],
      [656, 145, 138],
      [12, 150, 177],
      [150, 177, 188],...]
  </code></pre>
  
  <p>Now I want to erase the x values lower than 30 and y values that correspond with the erased x values. (For example, (x,y) = (1,12) in x[1] and y[1])</p>
  
  <p>In order to do that, I tried to use np.where in Numpy.</p>
  
  <p>I converted the x and y lists into arrays by using np.array and got this for x</p>
  
  <pre><code>array([None, list([11]), list([12, 11]), ..., list([12, 13]),list([13, 13]), list([13, 15])], dtype=object)
  </code></pre>
  
  <p>Then I used np.where(a&lt;30) and got this error</p>
  
  <pre><code>TypeError: '&gt;' not supported between instances of 'NoneType' and 'int'
  </code></pre>
  
  <p>I thought the None values in the first lists were the problem so I implemented</p>
  
  <pre><code>np.where(a[1:]&gt;30)
  </code></pre>
  
  <p>Then I got 
      TypeError: '>' not supported between instances of 'list' and 'int'</p>
  
  <p>I'm a beginner and want to know what caused this errors.</p>