How to label a line in matplotlib (python)?

Question

I followed the documentation but still failed to label a line.

plt.plot([min(np.array(positions)[:,0]), max(np.array(positions)[:,0])], [0,0], color='k', label='East') # West-East
plt.plot([0,0], [min(np.array(positions)[:,1]), max(np.array(positions)[:,1])], color='k', label='North') # South-North

In the code snippet above, I am trying to plot out the North direction and the East direction.

position contains the points to be plotted.

But I end up with 2 straight lines with NO labels as follows:

Where went wrong?

Answer 1

The argument label is used to set the string that will be shown in the legend. For example consider the following snippet:

  import matplotlib.pyplot as plt
  plt.plot([1,2,3],'r-',label='Sample Label Red')
  plt.plot([0.5,2,3.5],'b-',label='Sample Label Blue')
  plt.legend()
  plt.show()

This will plot 2 lines as shown:

The arrow function supports labels. Do check this link: http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.arrow