Legend placement and styling in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the position of the legend in this plot?

Consider the following matplotlib code that plots two lines and places a legend. What will be the location of the legend on the plot?

Matplotlib

import matplotlib.pyplot as plt

plt.plot([1, 2, 3], label='Line 1')
plt.plot([3, 2, 1], label='Line 2')
plt.legend(loc='upper left')
plt.show()

A The legend appears at the center of the plot area.

B The legend appears outside the plot area on the right side.

C The legend appears at the upper left corner of the plot area.

D The legend appears at the bottom right corner of the plot area.

💡 Hint

The 'loc' parameter controls the legend's position inside the plot area.

The 'loc' parameter in plt.legend() specifies the legend's position. 'upper left' places it at the top-left corner inside the plot.

❓ Predict Output

intermediate

What color and font size will the legend text have?

Given this code snippet, what will be the color and font size of the legend text?

Matplotlib

import matplotlib.pyplot as plt

plt.plot([1, 2, 3], label='Data')
plt.legend(fontsize=14, facecolor='lightgray', edgecolor='black')
plt.show()

A The legend text will be black with default font size, and the legend box will have a white background with no border.

B The legend text will be black with font size 14, and the legend box will have a light gray background with a black border.

C The legend text will be light gray with font size 14, and the legend box will have a black background with a light gray border.

D The legend text will be white with font size 14, and the legend box will have a light gray background with no border.

💡 Hint

facecolor sets the background color of the legend box, fontsize controls text size.

The fontsize parameter sets the legend text size to 14. facecolor='lightgray' sets the background color, and edgecolor='black' adds a black border. Text color defaults to black.

❓ visualization

advanced

Which legend style matches the plot output?

A plot has three lines with a legend placed outside the plot on the right side. The legend has a shadow and a semi-transparent background. Which code snippet produces this legend style?

Matplotlib

import matplotlib.pyplot as plt

plt.plot([1, 2, 3], label='A')
plt.plot([3, 2, 1], label='B')
plt.plot([2, 3, 1], label='C')
plt.legend(loc='center left', bbox_to_anchor=(1, 0.5), shadow=True, framealpha=0.5)
plt.show()

A plt.legend(loc='center left', bbox_to_anchor=(1, 0.5), shadow=True, framealpha=0.5)

B plt.legend(loc='upper right', shadow=True, framealpha=0.5)

C plt.legend(loc='best', bbox_to_anchor=(1, 1), shadow=False, framealpha=1)

D plt.legend(loc='lower left', bbox_to_anchor=(0, 0), shadow=True, framealpha=0)

💡 Hint

bbox_to_anchor moves the legend outside the plot area.

loc='center left' with bbox_to_anchor=(1, 0.5) places the legend outside the plot on the right center. shadow=True adds a shadow, framealpha=0.5 makes the background semi-transparent.

🔧 Debug

advanced

Why does this legend not appear on the plot?

This code plots two lines and tries to add a legend, but the legend does not show. What is the reason?

Matplotlib

import matplotlib.pyplot as plt

plt.plot([1, 2, 3])
plt.plot([3, 2, 1])
plt.legend()
plt.show()

A The plt.show() call is missing, so the plot and legend do not render.

B The plt.legend() call is missing the loc parameter, so the legend is hidden.

C The plt.plot() calls are missing color arguments, so the legend cannot be created.

D The plot lines have no labels, so the legend has nothing to display.

💡 Hint

Legend needs labels to show entries.

Without labels in plt.plot(), plt.legend() has no text to display, so the legend does not appear.

🚀 Application

expert

How to place a legend inside a plot with custom font and no frame?

You want to place a legend inside the plot at the lower center position. The legend text should be size 12 and blue. The legend box should have no frame or background color. Which code snippet achieves this?

A plt.legend(loc='lower center', fontsize=12, frameon=False, prop={'size':12, 'color':'blue'})

B plt.legend(loc='lower center', fontsize=12, framealpha=0, labelcolor='blue')

C plt.legend(loc='lower center', fontsize=12, frameon=False, prop={'color':'blue'})

D plt.legend(loc='lower center', fontsize=12, frameon=False, labelcolor='blue')

💡 Hint

Use 'prop' dictionary to style font properties including color and size.

frameon=False removes the legend frame. The 'prop' parameter accepts a dictionary for font properties like size and color. labelcolor is not a valid parameter for plt.legend.