Basic pie chart with plt.pie in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this pie chart code?

Consider this Python code using matplotlib to create a pie chart. What will be the displayed percentages on the pie slices?

Matplotlib

import matplotlib.pyplot as plt
sizes = [10, 20, 30]
labels = ['A', 'B', 'C']
plt.pie(sizes, labels=labels, autopct='%1.1f%%')
plt.show()

A Slices labeled A: 16.7%, B: 33.3%, C: 50.0%

B Slices labeled A: 25%, B: 25%, C: 50%

C Slices labeled A: 10%, B: 20%, C: 30%

D Slices labeled A: 20%, B: 30%, C: 50%

💡 Hint

Percentages are calculated as each size divided by the total sum of sizes.

The total sum is 10 + 20 + 30 = 60. So, A is 10/60 = 16.7%, B is 20/60 = 33.3%, and C is 30/60 = 50%.

❓ data_output

intermediate

How many slices will the pie chart have?

Given this code snippet, how many slices will the pie chart display?

Matplotlib

import matplotlib.pyplot as plt
sizes = [5, 15, 25, 55]
plt.pie(sizes)
plt.show()

A 1 slice

B 5 slices

C 3 slices

D 4 slices

💡 Hint

Each number in sizes corresponds to one slice.

The list sizes has 4 numbers, so the pie chart will have 4 slices.

❓ visualization

advanced

Which option produces a pie chart with exploded slices?

Look at these four code snippets. Which one will create a pie chart where each slice is slightly separated (exploded) from the center?

A plt.pie([10, 20, 30], explode=[0, 0, 0])

B plt.pie([10, 20, 30], explode=[1, 0, 0])

C plt.pie([10, 20, 30], explode=[0.1, 0.1, 0.1])

D plt.pie([10, 20, 30], explode=[0.1, 0, 0.1])

💡 Hint

The explode parameter controls how far each slice is offset from the center.

Only option C explodes all slices equally by 0.1, separating each slice from the center.

🔧 Debug

advanced

What error does this pie chart code raise?

This code tries to create a pie chart but fails. What error will it raise?

Matplotlib

import matplotlib.pyplot as plt
sizes = [10, 20]
labels = ['A', 'B', 'C']
plt.pie(sizes, labels=labels)
plt.show()

A TypeError: unsupported operand type(s) for +: 'int' and 'str'

B ValueError: 'labels' must be the same length as 'sizes'

C IndexError: list index out of range

D No error, pie chart displays with missing label

💡 Hint

Labels list length must match sizes list length exactly.

The labels list has 3 items but sizes has 2, causing a ValueError about mismatched lengths.

🚀 Application

expert

Which option produces a pie chart with a shadow and start angle at 90 degrees?

You want a pie chart that has a shadow effect and starts drawing slices from the top (90 degrees). Which code snippet does this correctly?

A plt.pie([15, 25, 60], shadow=True, startangle=90)

B plt.pie([15, 25, 60], shadow=False, startangle=0)

C plt.pie([15, 25, 60], shadow=True, startangle=0)

D plt.pie([15, 25, 60], shadow=False, startangle=90)

💡 Hint

The shadow parameter adds a shadow, startangle rotates the start position in degrees.

Option A sets shadow=True for shadow and startangle=90 to start slices from the top.

Practice

1. What does the plt.pie() function in matplotlib do?

easy

A. It creates a line chart to show trends over time.

B. It creates a pie chart to show parts of a whole.

C. It creates a bar chart to compare categories.

D. It creates a scatter plot to show data points.

Solution

1. Step 1: Understand the purpose of plt.pie()

   The function plt.pie() is designed to create pie charts, which visually represent parts of a whole as slices of a circle.

2. Step 2: Compare with other chart types

   Line charts, bar charts, and scatter plots are created with different functions like plt.plot(), plt.bar(), and plt.scatter(), not plt.pie().

3. Final Answer:

   It creates a pie chart to show parts of a whole. -> Option B

4. Quick Check:

   Pie chart = plt.pie() [OK]

Hint: Pie chart = parts of whole, use plt.pie() [OK]

Common Mistakes:

• Confusing pie chart with bar or line charts
• Thinking plt.pie() creates scatter plots
• Mixing up chart functions in matplotlib

2. Which of the following is the correct syntax to create a basic pie chart with labels using matplotlib?

easy

A. plt.pie(sizes, labels=labels)

B. plt.pie(labels, sizes=sizes)

C. plt.pie(labels=sizes, sizes=labels)

D. plt.pie(sizes, labels)

Solution

1. Step 1: Check the order of arguments in plt.pie()

   The first argument to plt.pie() is the sizes (values) of slices, and labels are passed as a keyword argument labels=.

2. Step 2: Validate correct keyword usage

   plt.pie(sizes, labels=labels) correctly uses plt.pie(sizes, labels=labels). Options B and C misuse argument order or keywords, and D misses the keyword for labels.

3. Final Answer:

   plt.pie(sizes, labels=labels) -> Option A

4. Quick Check:

   Sizes first, labels keyword [OK]

Hint: Sizes first, labels with labels= keyword [OK]

Common Mistakes:

• Passing labels as first argument instead of sizes
• Omitting labels= keyword
• Swapping sizes and labels arguments

3. What will be the output of this code?

import matplotlib.pyplot as plt
sizes = [30, 20, 50]
labels = ['A', 'B', 'C']
plt.pie(sizes, labels=labels, autopct='%1.1f%%')
plt.show()

medium

A. A pie chart with three slices labeled A, B, C showing percentages 30.0%, 20.0%, 50.0%

B. A bar chart with bars labeled A, B, C

C. A pie chart with slices but no labels or percentages

D. Syntax error due to autopct usage

Solution

1. Step 1: Understand plt.pie() parameters

   The sizes list defines slice sizes, labels assign names, and autopct='%1.1f%%' adds percentage text on slices.

2. Step 2: Predict the visual output

   The code will produce a pie chart with three slices labeled A, B, C, each showing their percentage values 30.0%, 20.0%, and 50.0% respectively.

3. Final Answer:

   A pie chart with three slices labeled A, B, C showing percentages 30.0%, 20.0%, 50.0% -> Option A

4. Quick Check:

   autopct adds percentages [OK]

Hint: autopct='%1.1f%%' shows slice percentages [OK]

Common Mistakes:

• Thinking autopct causes errors
• Expecting bar chart instead of pie chart
• Ignoring labels or percentages on chart

4. Identify the error in this code snippet that tries to create a pie chart:

import matplotlib.pyplot as plt
sizes = [40, 30, 30]
labels = ['X', 'Y', 'Z']
plt.pie(labels, sizes=sizes)
plt.show()

medium

A. The sizes list must be strings, not numbers.

B. The labels list is missing a keyword argument.

C. plt.show() is missing parentheses.

D. The sizes argument should be the first positional argument, not labels.

Solution

1. Step 1: Check argument order in plt.pie()

   The first argument must be sizes (numbers), but the code passes labels first, which is incorrect.

2. Step 2: Correct argument usage

   Sizes should be the first positional argument, and labels should be passed with labels=labels keyword.

3. Final Answer:

   The sizes argument should be the first positional argument, not labels. -> Option D

4. Quick Check:

   Sizes first, labels keyword [OK]

Hint: Sizes first, labels with labels= keyword [OK]

Common Mistakes:

• Passing labels as first argument
• Forgetting labels= keyword
• Confusing argument order

5. You want to create a pie chart showing sales distribution for 4 products with sizes [15, 25, 35, 25] and labels ['P1', 'P2', 'P3', 'P4']. You also want to highlight the largest slice by "exploding" it out. Which code correctly does this?

hard

A. plt.pie([15,25,35,25], labels=['P1','P2','P3','P4'], explode=[0,0,0,0.1], autopct='%1.1f%%')

B. plt.pie([15,25,35,25], labels=['P1','P2','P3','P4'], explode=[0.1,0,0,0], autopct='%1.1f%%')

C. plt.pie([15,25,35,25], labels=['P1','P2','P3','P4'], explode=[0,0,0.1,0], autopct='%1.1f%%')

D. plt.pie([15,25,35,25], labels=['P1','P2','P3','P4'], explode=[0,0.1,0,0], autopct='%1.1f%%')

Solution

1. Step 1: Identify the largest slice

   The sizes are [15, 25, 35, 25]. The largest value is 35 at index 2 (third element).

2. Step 2: Set explode to highlight largest slice

   The explode list should have 0.1 at index 2 and 0 elsewhere: [0, 0, 0.1, 0]. plt.pie([15,25,35,25], labels=['P1','P2','P3','P4'], explode=[0,0,0.1,0], autopct='%1.1f%%') matches this.

3. Final Answer:

   plt.pie([15,25,35,25], labels=['P1','P2','P3','P4'], explode=[0,0,0.1,0], autopct='%1.1f%%') -> Option C

4. Quick Check:

   Explode largest slice index 2 [OK]

Hint: Explode list: 0.1 at largest slice index [OK]

Common Mistakes:

• Exploding wrong slice index
• Using explode without matching list length
• Forgetting autopct for percentages