Labels, Titles & Legends

Reviewed & published by Brayan K

Matplotlib is a Python library for creating charts and visualizations — but a chart without labels is a puzzle, so this lesson is about making every plot explain itself.

Part of the free Matplotlib course at LearnCodingFast — hands-on lessons with worked examples and the output they print, plus practice exercises and a quick quiz.

You'll add axis labels and a title, attach a legend that names each line, and position that legend exactly where you want it.

What You'll Learn in This Lesson

• Labeling axes with xlabel and ylabel
• Adding a chart title with plt.title
• Naming lines with the label= argument
• Showing a legend with plt.legend()
• Positioning the legend with loc
• Why a labelled chart is easier to read

1 Axis Labels and a Title

Three calls turn an anonymous chart into a clear one: plt.xlabel(), plt.ylabel(), and plt.title(). Add them any time before plt.show().

📊 The three labelling calls

• plt.xlabel("...") — names the horizontal axis
• plt.ylabel("...") — names the vertical axis
• plt.title("...") — heading above the plot

import matplotlib.pyplot as plt

month = [1, 2, 3, 4, 5, 6]
sales = [120, 150, 170, 160, 200, 240]

plt.plot(month, sales)

plt.xlabel("Month")
plt.ylabel("Sales (units)")
plt.title("Monthly Sales")

plt.show()

What you'll see: a rising line, now with "Month" written under the x-axis, "Sales (units)" rotated along the y-axis, and a bold "Monthly Sales" heading centered above the chart.

2 Adding a Legend

When a chart has several lines, a legend tells the reader which is which. Give each line a label=, then call plt.legend() once.

import matplotlib.pyplot as plt

month = [1, 2, 3, 4, 5, 6]
online = [80, 95, 110, 130, 150, 180]
store = [120, 115, 100, 105, 95, 90]

plt.plot(month, online, label="Online")
plt.plot(month, store, label="In-store")

plt.xlabel("Month")
plt.ylabel("Sales (units)")
plt.title("Online vs In-store")
plt.legend()

plt.show()

What you'll see: two lines — Online climbing and In-store falling — with a small legend box in a corner that maps each color to its name, plus the axis labels and title from before.

3 Positioning the Legend

By default Matplotlib drops the legend wherever it fits, but you can place it precisely with the loc argument — for example 'upper left' or 'lower right'.

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
a = [1, 4, 9, 16, 25]
b = [2, 4, 6, 8, 10]

plt.plot(x, a, label="Squares")
plt.plot(x, b, label="Doubles")

plt.xlabel("x")
plt.ylabel("y")
plt.title("Growth Comparison")

# Pin the legend to the upper-left corner
plt.legend(loc="upper left")

plt.show()

What you'll see: the steep "Squares" curve and the gentler "Doubles" line, with the legend box anchored firmly in the top-left corner instead of floating wherever Matplotlib chooses.

🎯 Your Turn: Fill in the Blanks

Replace each ___ to fully label this chart and show a legend.

import matplotlib.pyplot as plt

week = [1, 2, 3, 4]
calories = [2100, 1950, 2200, 2050]

plt.plot(week, calories, label="Intake")

# Label the horizontal axis
plt.___("Week")

# Label the vertical axis
plt.ylabel("___")

# Add a heading
plt.title("___")

# Show the legend
plt.___()

plt.show()

📋 Common Errors & Quick Reference

❌ Legend is empty / "No artists with labels"

You called plt.legend() but never passed label= to your plots. Add a label to each line.

❌ Labels disappear after plt.show()

Add your labels and legend before plt.show(). Once the figure is shown it is cleared.

🏆 Mini Challenge: A Fully Labelled Chart

Plot two lines and add axis labels, a title, and a positioned legend.

import matplotlib.pyplot as plt

hour = [9, 10, 11, 12, 13, 14]
team_a = [5, 8, 12, 15, 14, 18]
team_b = [3, 6, 7, 11, 13, 16]

plt.plot(hour, team_a, label="Team A")
plt.plot(hour, team_b, label="Team B")

# 1. Axis labels
plt.xlabel("Hour")
plt.ylabel("Tasks done")

# 2. Title
plt.title("Tasks Completed by Hour")

# 3. Legend in the lower right
plt.legend(loc="lower right")

plt.show()

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
fig, ax = plt.subplots()
ax.plot(x, [2, 4, 6, 8], label="doubled")
ax.plot(x, [1, 4, 9, 16], label="squared")

ax.set_title("Two Series")
ax.set_xlabel("n")
ax.set_ylabel("value")
leg = ax.legend(loc="upper left", title="series")

print("Title: ", ax.get_title())
print("X label:", ax.get_xlabel())
print("Y label:", ax.get_ylabel())
print("Legend title:", leg.get_title().get_text())
print("Legend entries:", [t.get_text() for t in leg.get_texts()])
print("Entries match the labelled lines:", len(leg.get_texts()) == len(ax.lines))

# ✅ Expected output:
# Title:  Two Series
# X label: n
# Y label: value
# Legend title: series
# Legend entries: ['doubled', 'squared']
# Entries match the labelled lines: True

❓ Frequently Asked Questions

Lesson complete — your charts explain themselves!

You added axis labels and titles, named your lines, and placed a legend exactly where you wanted it.

Practice quiz

Continue this course

• Previous: Your First Line Plot
• Next: Markers, Line Styles & Colors — Control the look of your lines with colors, dashes, and markers
• Quick reference: Matplotlib cheat sheet › Labels & Legends

Frequently asked questions

How do I label the x and y axes?

Use plt.xlabel('text') for the horizontal axis and plt.ylabel('text') for the vertical axis. Add plt.title('text') for a chart heading above the plot.

How do I add a legend?

Pass a label= to each plot call, for example plt.plot(x, y, label='Sales'), then call plt.legend(). The legend box lists every line that has a label.

Why is my legend empty or missing?

plt.legend() only shows lines that were given a label= argument. If you call legend() without any labels, Matplotlib warns that there are no labelled artists and shows nothing.

Can I move the legend?

Yes. Pass loc to plt.legend(), such as plt.legend(loc='upper left') or loc='lower right'. You can also use loc='best' to let Matplotlib pick the least-crowded corner.