title: Index in numpy's array
body: <p>Now I'm reading the book &quot;Grokking Deep Learning&quot; and I've encountered a piece that I could to understant</p>
  <pre><code>import sys, numpy as np
  from keras.datasets import mnist
  (x_train, y_train), (x_test, y_test) = mnist.load_data()
  images, labels = (x_train[0:1000].reshape(1000,28*28) \
                                          255, y_train[0:1000])
  one_hot_labels = np.zeros((len(labels),10))
  for i,l in enumerate(labels):
      one_hot_labels[i][l] = 1 // this row i can't understant
  labels = one_hot_labels
  </code></pre>
  <p>How the index <strong>l</strong> in the arrive <strong>one_hot_labels</strong> can be array by own?
  Might that is basic Python but I can't get it</p>