Legends and Colors

Legends

Legends are needed when you plot multiple series. McKinney is clear about one gotcha here: passing label="..." to plot() doesn’t draw a legend by itself — you must still call ax.legend() afterwards, whether or not you set labels beforehand.

diagram How a legend gets built mermaid

  flowchart LR
  A["ax.plot(x, y1, label='square')"] --> C["ax.legend()"]
  B["ax.plot(x, y2, label='linear')"] --> C
  C --> D["Legend box appears, one entry per label"]

Each series' label, set at plot time, only becomes a visible legend once you call ax.legend().

Legend

import matplotlib.pyplot as plt
 
x = [1, 2, 3, 4, 5]
y1 = [1, 4, 9, 16, 25]
y2 = [1, 2, 3, 4, 5]
 
plt.figure(figsize=(7, 4))
plt.plot(x, y1, label="square")
plt.plot(x, y2, label="linear")
plt.title("Two series")
plt.xlabel("x")
plt.ylabel("y")
plt.legend()
plt.tight_layout()
plt.show()

Colors

Use:

• high-contrast colors
• colorblind-friendly palettes when possible
• consistent color meaning across charts

Custom color

import matplotlib.pyplot as plt
 
plt.figure(figsize=(7, 4))
plt.plot([1, 2, 3], [3, 2, 5], color="#1f77b4")
plt.title("Custom color")
plt.tight_layout()
plt.show()

Tip

Avoid using too many colors in one chart.

From the book

McKinney notes the loc argument on ax.legend() controls placement, and its default, "best", tries to find the spot that overlaps the least with your data. To hide one series from the legend without removing it from the plot, pass label="_nolegend_" (or simply no label at all) for that series.

Next

Continue to Saving Plots as Images to export your finished, labelled charts.

🧪 Try It Yourself

Exercise 1 – Label a series and show the legend

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Exercise 2 – Use a hex color code

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Exercise 3 – Hide a series from the legend

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