title: TypeError: ufunc 'add' did not contain a loop
body: <p>I use Anaconda and gdsCAD and get an error when all packages are installed correctly.
  Like explained here: <a href="http://pythonhosted.org/gdsCAD/">http://pythonhosted.org/gdsCAD/</a></p>
  
  <pre><code>TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('S32') dtype('S32') dtype('S32')
  </code></pre>
  
  <p>My imports look like this (In the end I imported everything):</p>
  
  <pre><code>import numpy as np
  from gdsCAD import *
  import matplotlib.pyplot as plt
  </code></pre>
  
  <p>My example code looks like this:</p>
  
  <pre><code>something = core.Elements()
  box=shapes.Box( (5,5),(1,5),0.5)
  core.default_layer = 1
  core.default_colors = 2
  something.add(box)
  something.show()
  </code></pre>
  
  <p>My error message looks like this:</p>
  
  <pre><code>---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-5-2f90b960c1c1&gt; in &lt;module&gt;()
   31 puffer_wafer = shapes.Circle((0.,0.), puffer_wafer_radius, puffer_line_thickness)
   32 bp.add(puffer_wafer)
  ---&gt; 33 bp.show()
   34 wafer = shapes.Circle((0.,0.), wafer_radius, wafer_line_thickness)
   35 bp.add(wafer)
  
  C:\Users\rpilz\AppData\Local\Continuum\Anaconda2\lib\site-packages\gdscad-0.4.5-py2.7.egg\gdsCAD\core.pyc in _show(self)
   80     ax.margins(0.1)
   81 
  ---&gt; 82     artists=self.artist()
   83     for a in artists:
   84         a.set_transform(a.get_transform() + ax.transData)
  
  C:\Users\rpilz\AppData\Local\Continuum\Anaconda2\lib\site-packages\gdscad-0.4.5-py2.7.egg\gdsCAD\core.pyc in artist(self, color)
  952         art=[]
  953         for p in self:
  --&gt; 954             art+=p.artist()
  955         return art
  956 
  
  C:\Users\rpilz\AppData\Local\Continuum\Anaconda2\lib\site-packages\gdscad-0.4.5-py2.7.egg\gdsCAD\core.pyc in artist(self, color)
  475         poly = lines.buffer(self.width/2.)
  476 
  --&gt; 477         return [descartes.PolygonPatch(poly, lw=0, **self._layer_properties(self.layer))]
  478 
  479 
  
  C:\Users\rpilz\AppData\Local\Continuum\Anaconda2\lib\site-packages\gdscad-0.4.5-py2.7.egg\gdsCAD\core.pyc in _layer_properties(layer)
  103         # Default colors from previous versions
  104         colors = ['k', 'r', 'g', 'b', 'c', 'm', 'y']
  --&gt; 105         colors += matplotlib.cm.gist_ncar(np.linspace(0.98, 0, 15))
  106         color = colors[layer % len(colors)]
  107         return {'color': color}
  
  TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('S32') dtype('S32') dtype('S32')    
  </code></pre>