title: label is not working in matplotlib scatter plot
body: <p>I am facing this Weird behavior of matplotlib scatter plot in which label is not working. Please see the code snippet below-</p>
  <pre><code>import matplotlib
  from mpl_toolkits.mplot3d import Axes3D
  import matplotlib.pyplot as plt
  import numpy as np
  
  def get_data():
      n = 10
      theta = np.linspace(-4 * np.pi, 4 * np.pi, n)
      z = np.linspace(-2, 2, n)
      r = z**2 + 1
      x = r * np.sin(theta)
      y = r * np.cos(theta)
      return x, y, z
  
  x, y, z = get_data()
  
  fig = plt.figure()
  ax = fig.add_subplot(111, projection='3d')
  ax.plot(x, y, z, c='r', marker='o', label='plot label')
  ax.scatter(x, y, z+1, c='b', marker='^', label='scatter label')
  
  ax.set_xlabel('x')
  ax.set_ylabel('y')
  ax.set_zlabel('z')
  ax.legend()
  plt.show()
  </code></pre>
  <p>The above code produces following plot (notice that the label corresponding to scatter plot is missing)-</p>
  <p><a href="https://i.stack.imgur.com/tmcxM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tmcxM.png" alt="enter image description here" /></a></p>
  <p>Surprisingly, I am getting following error if <code>ax.plot</code> is commented-</p>
  <pre><code>/usr/lib/pymodules/python2.7/matplotlib/axes.py:4747: UserWarning: No labeled objects found. Use label='...' kwarg on individual plots.
    warnings.warn(&quot;No labeled objects found. &quot;
  </code></pre>
  <p>Below is the information about the system-</p>
  <ul>
  <li>Python 2.7.6</li>
  <li>matplotlib version: 1.3.1</li>
  <li>Ubuntu 14.04 LTS 64 Bit</li>
  </ul>
  <p><strong>Any workaround to show the label of scatter plot, please?</strong></p>