Font size guidelines in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the font size of the title in this plot?

Consider the following matplotlib code that sets font sizes for different parts of a plot. What will be the font size of the plot's title?

Matplotlib

import matplotlib.pyplot as plt
plt.figure()
plt.title('Sample Title', fontsize=16)
plt.xlabel('X-axis', fontsize=12)
plt.ylabel('Y-axis', fontsize=12)
plt.show()

A 12

B 10

C 16

D 14

💡 Hint

Look at the fontsize argument inside the plt.title() function.

The font size for the title is explicitly set to 16 using the fontsize=16 argument in plt.title(). Other font sizes do not affect the title.

❓ data_output

intermediate

What is the font size of x-axis tick labels after this code?

Given the code below, what will be the font size of the x-axis tick labels?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [4, 5, 6])
for tick in ax.get_xticklabels():
    tick.set_fontsize(14)
plt.show()

A 12

B 14

C 10

D 16

💡 Hint

Check the loop where set_fontsize is called on each tick label.

The code sets the font size of each x-axis tick label to 14 explicitly using set_fontsize(14).

❓ visualization

advanced

Identify the font size used for the legend text

Look at the code below that creates a plot with a legend. What font size will the legend text have?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], label='Line 1')
plt.plot([3, 2, 1], label='Line 2')
plt.legend(fontsize='small')
plt.show()

A 8 (x-small)

B 12 (medium)

C 14 (large)

D 10 (small)

💡 Hint

The fontsize argument in plt.legend() can take string values like 'small'.

The legend font size is set to 'small', which corresponds to a font size of 10 in matplotlib's default settings.

🧠 Conceptual

advanced

Why use relative font sizes in matplotlib?

Which of the following is the best reason to use relative font sizes (like 'small', 'medium', 'large') instead of fixed numeric sizes in matplotlib?

A Relative sizes automatically adjust when changing figure size or DPI, keeping proportions consistent.

B Relative sizes prevent any font size changes from user input.

C Relative sizes allow using any font family without errors.

D Relative sizes are faster to render than numeric sizes.

💡 Hint

Think about how plots scale on different screens or when saved at different resolutions.

Using relative font sizes helps keep text readable and proportional when the figure size or resolution changes.

🔧 Debug

expert

Why does this font size setting not apply to axis labels?

Examine the code below. The user wants to set the font size of axis labels to 14, but the labels remain small. What is the cause?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.xlabel('X-axis')
plt.ylabel('Y-axis')
plt.rcParams['font.size'] = 14
plt.show()

A The font size is set after the labels are created, so it does not affect existing labels.

B The font size must be set using plt.xlabel(fontsize=14) instead of rcParams.

C rcParams['font.size'] only affects tick labels, not axis labels.

D The plot command overrides all font size settings.

💡 Hint

Consider when rcParams changes take effect relative to plot commands.

Changing rcParams['font.size'] after creating labels does not update their font size. It must be set before or labels recreated.

Practice

1. Why is it important to set font sizes in a matplotlib chart?

easy

A. To increase the chart size

B. To change the chart colors

C. To add more data points

D. To make the chart text clear and easy to read

Solution

1. Step 1: Understand the role of font size in charts

   Font size controls how big or small the text appears on the chart, affecting readability.

2. Step 2: Connect font size to clarity

   Clear and readable text helps viewers understand the chart easily without straining their eyes.

3. Final Answer:

   To make the chart text clear and easy to read -> Option D

4. Quick Check:

   Font size improves readability = D [OK]

Hint: Font size controls text clarity on charts [OK]

Common Mistakes:

• Confusing font size with chart colors
• Thinking font size changes data points
• Assuming font size changes chart dimensions

2. Which of the following is the correct way to set the font size of the title in matplotlib?

easy

A. plt.title('My Chart', fontsize=14)

B. plt.title('My Chart', size=14px)

C. plt.title('My Chart', font=14)

D. plt.title('My Chart', font_size='large')

Solution

1. Step 1: Recall matplotlib title font size syntax

   The correct parameter to set font size is fontsize with an integer value.

2. Step 2: Check each option for correct syntax

   plt.title('My Chart', fontsize=14) uses fontsize=14, which is correct. Others use invalid parameters or units.

3. Final Answer:

   plt.title('My Chart', fontsize=14) -> Option A

4. Quick Check:

   Use fontsize=number for title font size = C [OK]

Hint: Use fontsize=number to set font size in matplotlib [OK]

Common Mistakes:

• Using size=14px instead of fontsize=14
• Using font_size or font parameters incorrectly
• Adding units like 'px' which matplotlib does not accept

3. What will be the font size of the x-axis label in this code?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.xlabel('X Axis', fontsize=16)
plt.show()

medium

A. 16 points

B. Default font size (usually 10)

C. 12 points

D. No label will appear

Solution

1. Step 1: Identify the font size parameter in xlabel

   The code uses fontsize=16 in plt.xlabel, which sets the label font size to 16 points.

2. Step 2: Understand matplotlib default behavior

   Since fontsize is explicitly set, it overrides the default size (usually 10).

3. Final Answer:

   16 points -> Option A

4. Quick Check:

   Explicit fontsize=16 sets label size = A [OK]

Hint: Check fontsize parameter value to find label size [OK]

Common Mistakes:

• Assuming default size when fontsize is set
• Confusing label font size with tick font size
• Thinking label won't show without extra commands

4. Identify the error in this code that tries to set font sizes for ticks:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.tick_params(axis='x', labelsize=14)
plt.yticks(fontsize='large')
plt.show()

medium

A. plt.tick_params syntax is wrong

B. fontsize='large' is invalid for plt.yticks

C. plt.plot syntax is wrong

D. plt.show() is missing

Solution

1. Step 1: Check syntax for tick font sizes

   Matplotlib expects labelsize=int in tick_params, not fontsize='large' in plt.yticks.

2. Step 2: Identify which line has the error

   plt.yticks(fontsize='large') is invalid and will cause an error.

3. Final Answer:

   fontsize='large' is invalid for plt.yticks -> Option B

4. Quick Check:

   Use tick_params(labelsize=int) for ticks [OK]

Hint: Use plt.tick_params(labelsize=number) for tick font sizes [OK]

Common Mistakes:

• Using string values like 'large' for tick fontsize
• Thinking plt.tick_params syntax is wrong
• Ignoring error messages about parameter types

5. You want to create a plot with a large title, medium axis labels, and small tick labels for clarity. Which font size settings follow good font size guidelines?

hard

A. Title fontsize=14, labels fontsize=14, ticks fontsize=14

B. Title fontsize=8, labels fontsize=20, ticks fontsize=14

C. Title fontsize=20, labels fontsize=14, ticks fontsize=8

D. Title fontsize=8, labels fontsize=8, ticks fontsize=8

Solution

1. Step 1: Understand font size roles for clarity

   Title should be largest to stand out, axis labels medium for readability, ticks smallest to avoid clutter.

2. Step 2: Match options to guideline

   Title fontsize=20, labels fontsize=14, ticks fontsize=8 matches this pattern: 20 (large), 14 (medium), 8 (small). Others do not follow this order.

3. Final Answer:

   Title fontsize=20, labels fontsize=14, ticks fontsize=8 -> Option C

4. Quick Check:

   Large title, medium labels, small ticks = A [OK]

Hint: Title > labels > ticks in font size for clarity [OK]

Common Mistakes:

• Making tick labels larger than title
• Using same font size for all text elements
• Choosing too small font sizes causing unreadable text