How can I draw inline line labels in Matplotlib?

Drawing inline labels in Matplotlib helps create cleaner plots by placing labels directly on the lines instead of using a separate legend box. The labellines package provides the labelLines() method to achieve this effect.

Installation

First, install the required package ?

pip install matplotlib-label-lines

Basic Example

Here's how to create a plot with inline labels ?

import numpy as np
import matplotlib.pyplot as plt
from labellines import labelLines

# Set figure size
plt.figure(figsize=(8, 4))

# Create data
X = np.linspace(0, 1, 500)
A = [1, 2, 5, 10, 20]

# Plot multiple lines with labels
for a in A:
    plt.plot(X, np.arctan(a*X), label=str(a))

# Add inline labels to all lines
labelLines(plt.gca().get_lines(), zorder=2.5)

plt.title('Inline Line Labels Example')
plt.xlabel('X values')
plt.ylabel('arctan(a*X)')
plt.grid(True, alpha=0.3)
plt.show()

Customizing Label Positions

You can control where labels appear on each line ?

import numpy as np
import matplotlib.pyplot as plt
from labellines import labelLines

plt.figure(figsize=(8, 4))

# Create data
x = np.linspace(0, 10, 100)
lines_data = {
    'sin(x)': np.sin(x),
    'cos(x)': np.cos(x),
    'sin(2x)': np.sin(2*x)
}

# Plot lines
for label, y_data in lines_data.items():
    plt.plot(x, y_data, label=label)

# Add labels at specific positions (0.2, 0.5, 0.8 along the line)
labelLines(plt.gca().get_lines(), xvals=[2, 5, 8])

plt.title('Custom Label Positions')
plt.xlabel('X values')
plt.ylabel('Y values')
plt.grid(True, alpha=0.3)
plt.show()

Parameters

Benefits Over Traditional Legends

• Space efficient − No separate legend box needed
• Clear association − Labels are directly on the lines
• Customizable positioning − Control exact label placement
• Better readability − Especially useful with many lines

Conclusion

Inline line labels using labelLines() provide a cleaner alternative to traditional legends. Install the matplotlib-label-lines package and use labelLines(plt.gca().get_lines()) to automatically place labels on your plot lines.