title: Specifying NumPy Arrays with 2-Bit Dtype
body: <p>According to the docs, it's possible to specify different array dtypes:</p>
  
  <pre><code>dt = np.dtype('u1')   # 8-bit unsigned integer
  dt = np.dtype('i4')   # 32-bit signed integer
  dt = np.dtype('f8')   # 64-bit floating-point number
  dt = np.dtype('c16')  # 128-bit complex floating-point number
  dt = np.dtype('a25')  # 25-length zero-terminated bytes
  dt = np.dtype('U25')  # 25-character string
  </code></pre>
  
  <p>However, the smallest unsigned integer dtype is 8-bit. Is there a way to create a 2-bit unsigned integer dtype? </p>