title: unsupported format string passed to numpy.ndarray
body: <p>Let's say I have the array:</p>
  <pre><code>import numpy as np
  x = np.array([1.2334, 2.3455, 3.456], dtype=np.float32)
  </code></pre>
  <p>and want to print:</p>
  <pre><code>print('{:.2f}%'.format(x))
  </code></pre>
  <p>It gives me:</p>
  <pre><code>unsupported format string passed to numpy.ndarray.__format__
  </code></pre>