title: np.array() creates array of list-objects when given a multidimensional array, but should create 'normal' array
body: <p>something strange is happening when I try to transform a multidimensional list into a multidimensional array.
  Here an example code how it should look like and what my goal is. This example works:</p>
  
  <pre><code>array = [[1, 1], [2, 2]]
  array = np.array(array)
  print(array)
  </code></pre>
  
  <p>The output is as expected:</p>
  
  <pre><code>[[1 1]
   [2 2]]
  </code></pre>
  
  <p><strong>Now to my code that is going wrong and I don't know why.</strong> I need the numpy arrays later for matplotlib. building_polygons is a multidimensional array. It contains a list of polygons where each polygon contains a list of points and every point consist of an x,y z coordinate.</p>
  
  <pre><code>all_poly_x = []
  all_poly_y = []
  all_poly_z = []
  for polygon in building_polygons:
      poly_x = []
      poly_y = []
      poly_z = []
      for point in polygon:
          poly_x.append(point[0])
          poly_y.append(point[1])
          poly_z.append(point[2])
      poly_x.append(poly_x[0])  # closing polygon
      poly_y.append(poly_y[0])  # closing polygon
      poly_z.append(poly_z[0])  # closing polygon
  
      all_poly_x.append(poly_x)
      all_poly_y.append(poly_y)
      all_poly_z.append(poly_z)
  
  all_poly_x = np.array(all_poly_x)
  all_poly_y = np.array(all_poly_y)
  all_poly_z = np.array(all_poly_z)
  </code></pre>
  
  <p>The error happens when executing the np.array(...) comand. Instead of creating an numpy array as shown in the working example, the following is created for example all x values(I shortened it):</p>
  
  <pre><code>[
   list([388426.87, 388433.48, 388447.84, 388426.87, 388426.87])
   list([388424.21, 388450.45, 388412.13, 388424.21, 388424.21])
   ...
   list([388457.11, 388430.84, 388469.1, 388457.11, 388457.11])
   list([388467.0, 388496.0, 388491.0, 388467.0, 388467.0])
  ]
  </code></pre>
  
  <p><strong>So why is it creating an numpy array with list objects?</strong></p>