Custom legend entries in Matplotlib - Mini Project: Build & Apply

Custom legend entries

📖 Scenario: You are creating a simple line chart to compare sales data for two products over four quarters. You want to add a legend to explain the lines, but you want to customize the legend entries to use your own labels and colors.

🎯 Goal: Build a line chart with two lines and add a custom legend with your own labels and colors that do not depend on the plotted lines' default labels.

📋 What You'll Learn

Create two lists of sales data for Product A and Product B for four quarters.

Create a list of quarter labels for the x-axis.

Plot the sales data for both products using matplotlib's plot function.

Create a custom legend with exactly two entries using matplotlib.patches.Patch for the legend handles.

Use the custom legend handles and labels in plt.legend().

Display the plot with plt.show().

💡 Why This Matters

🌍 Real World

Custom legends help make charts clearer and more professional, especially when default labels are not descriptive or when you want to highlight specific information.

💼 Career

Data scientists and analysts often customize legends in reports and presentations to improve communication and make visualizations easier to understand.

1

Create sales data and quarter labels

Create a list called quarters with values ["Q1", "Q2", "Q3", "Q4"]. Create two lists called sales_a and sales_b with values [150, 200, 250, 300] and [180, 210, 260, 310] respectively.

Matplotlib

# Create the lists quarters, sales_a, and sales_b
# Your code here

Need a hint?

Use square brackets to create lists with the exact values given.

2

Plot sales data lines

Import matplotlib.pyplot as plt. Use plt.plot() to plot sales_a and sales_b against quarters. Use colors "blue" for sales_a and "green" for sales_b. Do not add labels to the plot lines.

Matplotlib

quarters = ["Q1", "Q2", "Q3", "Q4"]
sales_a = [150, 200, 250, 300]
sales_b = [180, 210, 260, 310]

# Import matplotlib.pyplot as plt
# Plot sales_a and sales_b against quarters with colors blue and green
# Your code here

Need a hint?

Use plt.plot(x, y, color="colorname") to plot lines with specific colors.

3

Create custom legend handles

Import matplotlib.patches.Patch. Create two variables blue_patch and green_patch as Patch objects with colors "blue" and "green" respectively. These will be used as custom legend handles.

Matplotlib

import matplotlib.pyplot as plt
from matplotlib.patches import Patch

quarters = ["Q1", "Q2", "Q3", "Q4"]
sales_a = [150, 200, 250, 300]
sales_b = [180, 210, 260, 310]

plt.plot(quarters, sales_a, color="blue")
plt.plot(quarters, sales_b, color="green")

# Create blue_patch and green_patch as Patch objects with colors blue and green
# Your code here

Need a hint?

Use Patch(color="colorname") to create a colored patch for the legend.

4

Add custom legend and display plot

Use plt.legend() with handles=[blue_patch, green_patch] and labels=["Product A Sales", "Product B Sales"] to add a custom legend. Then call plt.show() to display the plot.

Matplotlib

import matplotlib.pyplot as plt
from matplotlib.patches import Patch

quarters = ["Q1", "Q2", "Q3", "Q4"]
sales_a = [150, 200, 250, 300]
sales_b = [180, 210, 260, 310]

plt.plot(quarters, sales_a, color="blue")
plt.plot(quarters, sales_b, color="green")

blue_patch = Patch(color="blue")
green_patch = Patch(color="green")

# Add a custom legend with handles blue_patch and green_patch and labels "Product A Sales" and "Product B Sales"
# Display the plot
# Your code here

Need a hint?

Use plt.legend(handles=[...], labels=[...]) to create a custom legend. Then call plt.show() to display the plot.