python matplotlib dash-dot-dot – how to?

You can define custom dashes:

import matplotlib.pyplot as plt

line, = plt.plot([1,5,2,4], '-')
line.set_dashes([8, 4, 2, 4, 2, 4]) 
plt.show()

[8, 4, 2, 4, 2, 4] means

• 8 points on, (dash)
• 4 points off,
• 2 points on, (dot)
• 4 points off,
• 2 points on, (dot)
• 4 points off.

@Achim noted you can also specify the dashes parameter:

plt.plot([1,5,2,4], '-', dashes=[8, 4, 2, 4, 2, 4])
plt.show()

produces the same result shown above.