Pie chart color customization in Matplotlib - Step-by-Step Execution

Concept Flow - Pie chart color customization

Start: Prepare data

↓

Choose colors list

↓

Call plt.pie() with colors

↓

Render pie chart with chosen colors

↓

Display chart

The flow shows preparing data, selecting colors, applying them in the pie chart, and displaying the result.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
sizes = [30, 20, 50]
colors = ['red', 'green', 'blue']
plt.pie(sizes, colors=colors)
plt.show()

This code draws a pie chart with three slices colored red, green, and blue.

Execution Table

Step	Action	Input/Parameter	Effect/Result
1	Prepare data sizes	[30, 20, 50]	Data ready for pie chart
2	Define colors list	['red', 'green', 'blue']	Colors assigned to slices
3	Call plt.pie()	sizes=[30,20,50], colors=['red','green','blue']	Pie chart slices colored accordingly
4	Render pie chart	N/A	Pie chart with red, green, blue slices shown
5	Display chart	plt.show()	Chart window opens with colored pie

💡 All slices colored and chart displayed, execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
sizes	undefined	[30, 20, 50]	[30, 20, 50]	[30, 20, 50]	[30, 20, 50]
colors	undefined	undefined	['red', 'green', 'blue']	['red', 'green', 'blue']	['red', 'green', 'blue']

Key Moments - 2 Insights

Why do the colors not change if I don't pass the colors parameter?

Without the colors parameter, matplotlib uses default colors. See execution_table step 3 where colors are explicitly passed to change slice colors.

What happens if the colors list length doesn't match the data size?

Matplotlib cycles through colors if fewer colors than slices are given. This is why colors list length should match sizes for clear mapping, as shown in execution_table step 2.

Visual Quiz - 3 Questions

Look at the execution table, what color is assigned to the second slice?

A red

B blue

C green

D default color

💡 Hint

Check the colors list in execution_table step 2 and 3.

At which step is the colors list defined?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' and 'Input/Parameter' columns in execution_table.

If you remove the colors parameter in plt.pie(), what will happen?

A The slices will all be the same color

B Matplotlib will use default colors for slices

C The pie chart will not display

D An error will occur

💡 Hint

Refer to key_moments about default color behavior.

Concept Snapshot

Pie chart color customization in matplotlib:
- Use plt.pie(data, colors=colors_list)
- colors_list must match data length for clear mapping
- If colors not given, default colors apply
- Colors can be named strings or hex codes
- Call plt.show() to display the chart

Full Transcript

This visual execution traces how to customize pie chart colors in matplotlib. First, data sizes are prepared as a list of values. Then, a colors list is defined with color names matching each slice. The plt.pie() function is called with sizes and colors parameters, which applies the colors to each slice in order. Finally, plt.show() displays the pie chart with the chosen colors. Key points include that colors must be passed explicitly to override defaults, and the colors list length should match the data length for clarity. The execution table shows each step and the variable states. The quiz tests understanding of color assignment and parameter usage.

Practice

1. What does the colors parameter do in a matplotlib pie chart?

easy

A. It changes the size of the pie chart.

B. It changes the chart title.

C. It adds labels to the pie slices.

D. It sets the colors of each slice in the pie chart.

Solution

1. Step 1: Understand the role of colors in pie charts

   The colors parameter is used to specify the colors for each slice of the pie chart.

2. Step 2: Compare with other options

   Options A, C, and D relate to size, labels, and title, which are controlled by other parameters.

3. Final Answer:

   It sets the colors of each slice in the pie chart. -> Option D

4. Quick Check:

   colors parameter = slice colors [OK]

Hint: Remember: colors parameter controls slice colors [OK]

Common Mistakes:

• Confusing colors with labels
• Thinking colors change chart size
• Mixing colors with title settings

2. Which of the following is the correct way to set colors in a matplotlib pie chart?

easy

A. plt.pie(data, colors=['red', 'blue', 'green'])

B. plt.pie(data, color=['red', 'blue', 'green'])

C. plt.pie(data, col=['red', 'blue', 'green'])

D. plt.pie(data, set_colors=['red', 'blue', 'green'])

Solution

1. Step 1: Recall the correct parameter name

   The correct parameter to set slice colors is colors, not color, col, or set_colors.

2. Step 2: Check syntax correctness

   plt.pie(data, colors=['red', 'blue', 'green']) uses colors with a list of color names, which is the correct syntax.

3. Final Answer:

   plt.pie(data, colors=['red', 'blue', 'green']) -> Option A

4. Quick Check:

   Use colors= list for slice colors [OK]

Hint: Use exact parameter name 'colors' for slice colors [OK]

Common Mistakes:

• Using 'color' instead of 'colors'
• Using undefined parameters like 'col' or 'set_colors'
• Passing colors as a string instead of a list

3. What will be the color of the second slice in this code?

import matplotlib.pyplot as plt
sizes = [30, 40, 30]
colors = ['#FF0000', '#00FF00', '#0000FF']
plt.pie(sizes, colors=colors)
plt.show()

medium

A. Blue

B. Red

C. Green

D. Black

Solution

1. Step 1: Identify the colors list order

   The colors list is ['#FF0000', '#00FF00', '#0000FF'], which correspond to red, green, and blue in order.

2. Step 2: Match the second slice color

   The second slice uses the second color '#00FF00', which is green.

3. Final Answer:

   Green -> Option C

4. Quick Check:

   Second color in list = green [OK]

Hint: Colors list order matches slice order [OK]

Common Mistakes:

• Mixing hex codes with color names
• Assuming default colors override given list
• Confusing slice index starting at 0 or 1

4. Find the error in this pie chart color code:

import matplotlib.pyplot as plt
sizes = [25, 25, 50]
colors = 'red, blue, green'
plt.pie(sizes, colors=colors)
plt.show()

medium

A. colors should be a list, not a string

B. sizes list has wrong values

C. plt.pie does not accept colors parameter

D. Missing plt.show() call

Solution

1. Step 1: Check the type of colors parameter

   The colors parameter must be a list of color names or hex codes, but here it is a single string.

2. Step 2: Understand the impact of wrong type

   Passing a string will cause matplotlib to treat it as one color or raise an error.

3. Final Answer:

   colors should be a list, not a string -> Option A

4. Quick Check:

   colors must be list, not string [OK]

Hint: Always pass colors as a list, not a single string [OK]

Common Mistakes:

• Passing colors as comma-separated string
• Ignoring type requirements for colors
• Assuming plt.show() is optional

5. You want to create a pie chart with 4 slices and use custom colors: red, green, blue, and yellow. Which code correctly applies these colors and also adds labels for each slice?

hard

A. plt.pie([10, 20, 30, 40], colors=['red', 'green', 'blue', 'yellow'], label=['A', 'B', 'C', 'D'])

B. plt.pie([10, 20, 30, 40], colors=['red', 'green', 'blue', 'yellow'], labels=['A', 'B', 'C', 'D'])

C. plt.pie([10, 20, 30, 40], colors=['red', 'green', 'blue'], labels=['A', 'B', 'C', 'D'])

D. plt.pie([10, 20, 30, 40], color=['red', 'green', 'blue', 'yellow'], labels=['A', 'B', 'C', 'D'])

Solution

1. Step 1: Verify the colors parameter and list length

   The colors parameter must be named exactly 'colors' and have 4 colors for 4 slices.

2. Step 2: Check the labels parameter name and length

   The labels parameter must be named 'labels' and have 4 labels matching the slices.

3. Step 3: Identify errors in other options

   plt.pie([10, 20, 30, 40], color=['red', 'green', 'blue', 'yellow'], labels=['A', 'B', 'C', 'D']) uses 'color' instead of 'colors'. plt.pie([10, 20, 30, 40], colors=['red', 'green', 'blue'], labels=['A', 'B', 'C', 'D']) has only 3 colors for 4 slices. plt.pie([10, 20, 30, 40], colors=['red', 'green', 'blue', 'yellow'], label=['A', 'B', 'C', 'D']) uses 'label' instead of 'labels'.

4. Final Answer:

   plt.pie([10, 20, 30, 40], colors=['red', 'green', 'blue', 'yellow'], labels=['A', 'B', 'C', 'D']) -> Option B

5. Quick Check:

   Use colors= and labels= with matching list lengths [OK]

Hint: Match colors and labels list lengths with data slices [OK]

Common Mistakes:

• Using wrong parameter names like 'color' or 'label'
• Mismatched list lengths for colors or labels
• Forgetting to pass labels parameter