title: What is the meaning of arr[:] in assignment in numpy?
body: <p>I occasionally use <code>numpy</code>, and I'm trying to become smarter about how I vectorize operations. I'm reading some code and trying to understand the semantics of the following:</p>
  
  <pre><code>arr_1[:] = arr_2
  </code></pre>
  
  <p>In this case, </p>
  
  <p>I understand that in <code>arr[:, 0]</code>, we're selecting the first column of the array, but I'm confused about what the difference is between <code>arr_1[:] = arr_2</code> and <code>arr_1 = arr_2</code></p>