Arrow annotations in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of arrow annotation coordinates

What will be the coordinates of the arrow's start and end points in this plot code?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])
arrow = ax.annotate('', xy=(0.8, 0.8), xytext=(0.2, 0.2), arrowprops=dict(facecolor='blue'))
print(f"Start: {arrow.xytext}, End: {arrow.xy}")

A Start: (0.8, 0.8), End: (0.2, 0.2)

B Start: (0.2, 0.8), End: (0.8, 0.2)

C Start: (0, 0), End: (1, 1)

D Start: (0.2, 0.2), End: (0.8, 0.8)

💡 Hint

Remember xytext is the start point and xy is the end point of the arrow.

The arrow starts at xytext=(0.2, 0.2) and points to xy=(0.8, 0.8).

❓ data_output

intermediate

Number of arrows in a plot

Given this code with multiple arrow annotations, how many arrows will be drawn on the plot?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
for i in range(3):
    ax.annotate('', xy=(i+1, i+1), xytext=(i, i), arrowprops=dict(facecolor='red'))
print(len(ax.texts))

A 1

B 6

C 3

D 0

💡 Hint

Each annotate call adds one arrow annotation.

The loop runs 3 times, each time adding one arrow annotation, so total 3 arrows.

❓ visualization

advanced

Effect of different arrow styles

Which option shows the correct arrow style applied to the annotation?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])
ax.annotate('Point', xy=(0.7, 0.7), xytext=(0.3, 0.3), arrowprops=dict(arrowstyle='->', color='green'))
plt.show()

A Arrow with a simple line and a triangular head pointing to the point

B Arrow with a circular head and dashed line

C Arrow with a double-headed style

D Arrow with no head, just a line

💡 Hint

The arrowstyle '->' means a simple arrow with a triangular head.

The arrowstyle '->' creates a line with a single triangular arrowhead pointing to the xy point.

🔧 Debug

advanced

Identify the error in arrow annotation code

What error will this code produce when run?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.annotate('Test', xy=(0.5, 0.5), xytext=(0.2, 0.2), arrowprops=dict(facecolor='red', shrink=1.5))
plt.show()

A SyntaxError due to missing colon

B TypeError: 'shrink' must be between 0 and 1

C No error, plot shows arrow with shrink applied

D ValueError: xy and xytext must be tuples

💡 Hint

Check the valid range for the 'shrink' parameter in arrowprops.

The 'shrink' parameter must be between 0 and 1. 1.5 is invalid and causes a TypeError.

🚀 Application

expert

Creating a custom curved arrow annotation

Which code snippet correctly creates a curved arrow annotation from (0.1, 0.1) to (0.9, 0.9) with a curved style?

A ax.annotate('', xy=(0.9, 0.9), xytext=(0.1, 0.1), arrowprops=dict(arrowstyle='->', connectionstyle='arc3,rad=0.3'))

B ax.annotate('', xy=(0.9, 0.9), xytext=(0.1, 0.1), arrowprops=dict(arrowstyle='-|>', connectionstyle='arc,rad=1.5'))

C ax.annotate('', xy=(0.1, 0.1), xytext=(0.9, 0.9), arrowprops=dict(arrowstyle='->', connectionstyle='arc3,rad=-0.3'))

D ax.annotate('', xy=(0.9, 0.9), xytext=(0.1, 0.1), arrowprops=dict(arrowstyle='->', connectionstyle='arc3,rad=3'))

💡 Hint

The connectionstyle 'arc3,rad=0.3' creates a gentle curved arrow.

Option A uses correct xy and xytext points and a valid connectionstyle with a reasonable curvature radius.