import matplotlib as mpl
import matplotlib.pyplot as plt

# high dpi so you can see the difference
fig, ax = plt.subplots(dpi=600)

# iterate through styles
for i, js in enumerate(("miter", "round", "bevel"), start=1):
    arrow_head = mpl.patches.ArrowStyle.CurveFilledAB(head_length=4, head_width=2)
    connection = mpl.patches.ConnectionStyle.Bar(fraction=0, angle=-90)
    double_arrow = mpl.patches.FancyArrowPatch((0.1 * i, 1 - 0.1), (1 - 0.1, 0.1 * i), linewidth=2,
                                       arrowstyle=arrow_head, connectionstyle=connection, joinstyle=js)
    ax.add_patch(double_arrow)