title: Strange output in matplotlib
body: <p>Can someone explain why I get this strange output when running this code:</p>
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  def x_y():
      return np.random.randint(9999, size=1000), np.random.randint(9999, size=1000)
  plt.plot(x_y())
  plt.show()
  </code></pre>
  <p>The output:</p>
  <p><a href="https://i.stack.imgur.com/s1VNe.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/s1VNe.jpg" alt="Output of the program" /></a></p>