Text annotations in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of annotation with xytext and arrowprops

What will be the output of this code snippet that uses matplotlib to annotate a point with an arrow and custom text position?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3], [1, 4, 9])
ax.annotate('Square', xy=(2, 4), xytext=(3, 7), arrowprops=dict(facecolor='blue', shrink=0.05))
plt.show()

A A plot with points connected by a line and an annotation 'Square' pointing to (2,4) with an arrow starting at (3,7) in blue color.

B A plot with points connected by a line and an annotation 'Square' at (2,4) without any arrow.

C A plot with points connected by a line and an annotation 'Square' at (3,7) without any arrow.

D A plot with points connected by a line and an annotation 'Square' pointing to (3,7) with an arrow starting at (2,4) in red color.

💡 Hint

Look at the parameters xy and xytext in the annotate function and the color specified in arrowprops.

The annotate function places the text at xytext coordinates (3,7) and draws an arrow pointing to xy coordinates (2,4). The arrow color is set to blue by facecolor='blue'.

❓ data_output

intermediate

Number of annotations in a plot

Given the following code, how many annotations will be visible on the plot?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0, 1, 2], [0, 1, 4])
ax.annotate('Start', xy=(0, 0))
ax.annotate('Middle', xy=(1, 1), xytext=(1, 2))
ax.annotate('End', xy=(2, 4), xytext=(2, 5), arrowprops=dict(arrowstyle='->'))
plt.show()

A 2

B 3

C 1

D 0

💡 Hint

Each call to annotate adds one annotation regardless of arrow presence.

There are three calls to annotate, so three annotations appear: 'Start' at (0,0), 'Middle' at (1,2), and 'End' at (2,5) with an arrow pointing to (2,4).

🔧 Debug

advanced

Identify the error in annotation code

What error will this code raise when executed?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3], [1, 4, 9])
ax.annotate('Point', xy=(2, 4), xytext=(3, 7), arrowprops={'color': 'green'})
plt.show()

A No error, the plot shows annotation with a green arrow.

B SyntaxError due to incorrect dictionary syntax in arrowprops.

C KeyError because 'color' is not a valid key in arrowprops.

D TypeError because arrowprops must be a list, not a dict.

💡 Hint

Check the valid keys for arrowprops in matplotlib annotations.

The arrowprops dictionary does not accept 'color' as a key. The correct key to set arrow color is facecolor or edgecolor. Using 'color' causes a KeyError.

❓ visualization

advanced

Effect of different arrow styles in annotations

Which option shows the correct arrow style for the annotation with arrowstyle='fancy'?

Matplotlib

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])
ax.annotate('Fancy Arrow', xy=(1, 1), xytext=(0, 0), arrowprops=dict(arrowstyle='fancy'))
plt.show()

A An arrow with a double-headed style connecting (0,0) to (1,1).

B A simple straight arrow with a line and a triangular head connecting (0,0) to (1,1).

C No arrow is drawn, only the text at (0,0).

D An arrow with a filled triangular head and a curved tail connecting (0,0) to (1,1).

💡 Hint

The fancy arrow style has a filled head and a curved tail.

The fancy arrow style draws an arrow with a filled triangular head and a curved tail, making it visually distinct from a simple arrow.

🧠 Conceptual

expert

Understanding coordinate systems in annotations

In matplotlib annotations, what coordinate system does the xycoords='axes fraction' parameter refer to?

A Coordinates are given as a fraction of the axes width and height, ranging from 0 to 1.

B Coordinates are given in data units of the plotted data.

C Coordinates are given relative to the entire screen resolution.

D Coordinates are given in pixels relative to the figure window.

💡 Hint

Think about how fractions relate to the axes size.

The axes fraction coordinate system means coordinates are fractions of the axes dimensions, where (0,0) is bottom-left and (1,1) is top-right of the axes area.