PYTHON

matplotlib

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Importing

matplotlib, just like numpy, is one of those libraries which has so much legacy behind the import statement that it’s worth breaking Python style rules and using the at keyword to change the name of the imported library. Traditionally, matplotlib.pyplot is imported as plt, with the statement:

import matplotlib.pyplot as plt

Using subplots

# Create two plots, in a grid with 2 rows and 1 column
# (plots will be stacked vertically)
fig, axs = plt.subplots(1, 2)

ax1 = axs[0]
ax2 = axs[1]

# Use each axX object normally...

Two Y-Axis Example

import matplotlib.pyplot as plt
import numpy as np

x = np.arange(0, 10, 0.1)
y1 = x**2
y2 = np.sin(x)

fig, ax1 = plt.subplots()

ax2 = ax1.twinx()

ax1.plot(x, y1, color='g')
ax2.plot(x, y2, color='b')

fig.suptitle('Two Y-Axis Example')
ax1.set_xlabel('x')
ax1.set_ylabel('y1')
ax2.set_ylabel('y2')

plt.show()

This will produce the following graph:

Example matplotlib graph using two separate Y-axis.

Example matplotlib graph using two separate Y-axis.

Matching The Legend Text Color To The Plot Line Color

It can be a handy visual aid to set the legend color to the same color as the corresponding line on the plot. This can be done with the following code:

fig, ax = plt.subplots()

x = np.linspace(0, 10, 100)
y_x = x
y_2x = 2*x
y_3x = 3*x

ax.plot(x, y_x, label='$y = x$')
ax.plot(x, y_2x, label='$y = 2x$')
ax.plot(x, y_3x, label='$y = 3x$')

leg = ax.legend()

# Set legend text color to line color
for line, text in zip(leg.get_lines(), leg.get_texts()):
    text.set_color(line.get_color())

plt.title('Legend Text Color Matches Plot Line Color')

plt.savefig('legend-text-color-matches-plot-line-color.png')

This will produce a plot which looks like:

Creating Animated Plots

When using the pillow writer, the GIF will not loop. When using the imagemagick writer, the GIF will loop.


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