Creating Custom Figure Subclasses in Matplotlib

Introduction

In this lab, you will learn how to create custom figure subclasses in Matplotlib. You will create a WatermarkFigure class that adds a text watermark to the plot.

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Skills Graph

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Import necessary libraries

First, import the necessary libraries: matplotlib.pyplot and numpy.

import matplotlib.pyplot as plt
import numpy as np

Create a custom figure subclass

Create a custom figure subclass called WatermarkFigure that adds a text watermark to the plot. This class inherits from the Figure class of Matplotlib.

from matplotlib.figure import Figure

class WatermarkFigure(Figure):
    """A figure with a text watermark."""

    def __init__(self, *args, watermark=None, **kwargs):
        super().__init__(*args, **kwargs)

        if watermark is not None:
            bbox = dict(boxstyle='square', lw=3, ec='gray',
                        fc=(0.9, 0.9, .9, .5), alpha=0.5)
            self.text(0.5, 0.5, watermark,
                      ha='center', va='center', rotation=30,
                      fontsize=40, color='gray', alpha=0.5, bbox=bbox)

Create data for the plot

Create some data for the plot. In this example, we will create x and y arrays using the numpy library.

x = np.linspace(-3, 3, 201)
y = np.tanh(x) + 0.1 * np.cos(5 * x)

Plot the data using custom figure subclass

Use the plt.figure() function to plot the data using the custom figure subclass WatermarkFigure. In this example, we will add the watermark text "draft" to the plot.

plt.figure(FigureClass=WatermarkFigure, watermark='draft')
plt.plot(x, y)

Review references

Review the references used in this example.

## References
## matplotlib.pyplot.figure
## matplotlib.figure.Figure
## matplotlib.figure.Figure.text

Summary

In this lab, you learned how to create a custom figure subclass in Matplotlib. You created a WatermarkFigure class that adds a text watermark to the plot. You also learned how to plot data using the custom figure subclass.