matplotlib simple and two head arrows

You can draw two one-headed arrows along the same line but in opposite directions.

import matplotlib.pyplot as plt
# Arrows
plt.arrow(0.3, 0.1, 0.4, 0.7, color='red', head_length = 0.07, head_width = 0.025, length_includes_head = True)
plt.arrow(0.7, 0.8, -0.4, -0.7, color='red', head_length = 0.07, head_width = 0.025, length_includes_head = True)
plt.show()

You can create double-headed arrows by plotting two plt.arrow which are overlapping. The code below helps to do that.

import matplotlib.pyplot as plt

plt.figure(figsize=(12,6))

# red arrow
plt.arrow(0.15, 0.5, 0.75, 0, head_width=0.05, head_length=0.03, linewidth=4, color='r', length_includes_head=True)

# green arrow
plt.arrow(0.85, 0.5, -0.70, 0, head_width=0.05, head_length=0.03, linewidth=4, color='g', length_includes_head=True)

plt.show()

And the result is like this:

You can see that the red arrow is being plotted firstly, and then the green one. When you supply the correct coordinates, it looks like a double-headed.

You can use matplotlib.patches.FancyArrowPatch to draw a two-headed arrow. This class allows to specify arrowstyle:

import matplotlib.patches as patches

p1 = patches.FancyArrowPatch((0, 0), (1, 1), arrowstyle='<->', mutation_scale=20)
p2 = patches.FancyArrowPatch((1, 0), (0, 1), arrowstyle='<|-|>', mutation_scale=20)

This produces the following arrows:

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()