How do I place an arrow at the end of a curve in matplotlib?

The FancyArrowPatch class takes a path as an argument, so I thought you could use that.

1) For each line segment, create an instance matplotlib.path.Path

.

2) Use an instance of the path to draw an arrow.

import numpy as np
import matplotlib.pyplot as plt; plt.ion()
from matplotlib.patches import FancyArrowPatch, PathPatch
from matplotlib.path import Path

def create_path(x,y):
    vertices = zip(x,y)
    codes = [Path.MOVETO] + (len(vertices)-1) * [Path.CURVE3]
    return Path(vertices, codes)

X = np.linspace(0,4*np.pi,10000)
Y = np.sin(X)

fig, ax = plt.subplots(1,1)
ax.plot(X,Y,color='blue')

shift = 0.1
seg_size = 300

i = 0
while i +seg_size < len(X):
    x = X[i:i+seg_size]
    y = Y[i:i+seg_size]+shift

    path = create_path(x,y)

    # for testing path 
    # patch = PathPatch(path, facecolor='none', lw=2)
    # ax.add_patch(patch)

    arrow = FancyArrowPatch(path=path, color='r')
    ax.add_artist(arrow)

    i += seg_size*2

      

        
        
        
      

    

Unfortunately, this does not work as the path that is passed to FancyArrowPatch cannot contain more than two segments (not documented, but there is a check ensure_quadratic_bezier

).

So you have to cheat. Below, I use the last 2 points of each segment to draw an arrow.

import numpy as np
import matplotlib.pyplot as plt; plt.ion()
from matplotlib.patches import FancyArrowPatch

X = np.linspace(0,4*np.pi,10000)
Y = np.sin(X)

fig, ax = plt.subplots(1,1)
ax.plot(X,Y,color='blue')

shift = 0.1
seg_size = 300

i = 0
while i +seg_size < len(X):
    x = X[i:i+seg_size]
    y = Y[i:i+seg_size]+shift

    ax.plot(x, y, 'k')

    posA, posB = zip(x[-2:], y[-2:])
    edge_width = 2.
    arrowstyle = "fancy,head_length={},head_width={},tail_width={}".format(2*edge_width, 3*edge_width, edge_width)
    arrow = FancyArrowPatch(posA=posA, posB=posB, arrowstyle=arrowstyle, color='k')
    ax.add_artist(arrow)

    i += seg_size*2