Python:Matplotlib .fill()

The .fill() function in Matplotlib fills the area enclosed by specified x and y coordinates with color. It’s often used to highlight or emphasize regions defined by one or more polygons on a plot.

Syntax

matplotlib.pyplot.fill(*args, data=None, **kwargs)

Parameters:

• *args: One or more pairs of x and y coordinates defining the polygons to fill.
• data: An object (like a DataFrame or dict) that provides named variables for x and y.
• **kwargs: Additional keyword arguments controlling the fill style, such as:
  • color or facecolor: Fill color.
  • edgecolor: Color of the polygon edge.
  • linewidth: Width of polygon edges.
  • alpha: Transparency level (0.0 to 1.0).
  • Any other valid Polygon properties.

Return value:

Returns a list of matplotlib.patches.Polygon objects representing the filled regions.

Example 1: Filling a Rectangle Shape

This example fills the area enclosed by a rectangle:

import matplotlib.pyplot as plt

x = [0, 3, 3, 0]
y = [0, 0, 3, 3]

plt.fill(x, y, color='green', alpha=0.75)
plt.title('Filled Rectangle')
plt.show()

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The output of this code is:

Example 2: Filling Custom Polygon Shapes

This example fills two different polygons using custom edge and fill colors:

import matplotlib.pyplot as plt

# Polygon 1
a = [0, 1, 2, 1]
b = [0, 2, 0, -2]
plt.fill(a, b, color='skyblue', edgecolor='red', linewidth=2)

# Polygon 2
m = [0, 0, 3, 3]
n = [0, 3, 0, 3]
plt.fill(m, n, color='pink', alpha=0.6)

plt.title('Custom Filled Polygons')
plt.show()

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The output of this code is: