python - matplotlib simple and two head arrows

Question

I would like to make a simple arrow and a two head arrow. I used the following to make a simple arrow, but I doubt this is the easiest method :

import matplotlib.pyplot as plt
arr_width = .009   #  I don't know what unit it is here.
fig = plt.figure()
ax1 = fig.add_subplot(111)
ax1.plot(range(10))
ax1.arrow(1, 1, 0, .5, width = arr_width, head_width = 3 * arr_width, 
          head_length = 9 * arr_width)
plt.show()

I can't find how to make two head arrows with this method.

Answer 1

You can create a double-headed arrow using the annotate method with blank text annotation and setting the arrowprops dict to include arrowstyle='<->' as shown below:

import matplotlib.pyplot as plt

plt.annotate(s='', xy=(1,1), xytext=(0,0), arrowprops=dict(arrowstyle='<->'))

plt.show()