title: No conversion path for dtype ('<U1') issue
body: <p>I have a 2d list (Data_set) that contain a 3d array and a label(0 or 1), I want to make the h5py file with two datasets one for 3d array and the other for the label, this is my code for doing that:
  `</p>
  
  <pre><code>    data = []
      label = []
      for i in range(len(Data_set)):
          data.append(Data_set[i][0])# 3d array
          label.append(Data_set[i][1])#label
      data = np.array(data)
      label = np.array(label)
      dt = np.dtype('int16')
      with h5py.File(output_path+'dataset.h5', 'w') as hf:
          hf.create_dataset('data',dtype=dt ,data=data, compression='lzf')
          hf.create_dataset('label', dtype=dt, data=label, compression='lzf')
  </code></pre>
  
  <p>`
  the content of the 2d list is shown in the image below:
  <a href="https://i.stack.imgur.com/A9HWj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/A9HWj.png" alt="enter image description here"></a>
  but when I run the code it gives me an error: see the image below
  <a href="https://i.stack.imgur.com/ldCfL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ldCfL.png" alt="enter image description here"></a>
  please help me to solve the problem?</p>