使用 matplotlib 将图例中的标记与图例标题左对齐

Question

I'm trying to make a plot with Matplotlib, and I would look to have the legend on the top left. Without a legend title this is working fine with the code below, but when I add a legend title which is longer than the legend labels, the markers shift.

Is there any way I can prevent this and have them all align to the left?

import numpy as np
import matplotlib.pyplot as plt

# Data
x = np.arange(0, 4 * np.pi ,0.1)
y = np.sin(x)

fig, axs = plt.subplots(1, 2, figsize=(8, 4))

# Working fine without legend title
axs[0].plot(x, y, label='sin')
axs[0].legend(title='', loc='lower left', bbox_to_anchor=(0,1), facecolor='white', edgecolor='white', framealpha=1)

# Position shifts when using long legend title
axs[1].plot(x, y, label='sin')
axs[1].legend(title='Some longer title', loc='lower left', bbox_to_anchor=(0,1), facecolor='white', edgecolor='white', framealpha=1)

plt.show()

Answer 1

For me, your code does something similar to what you want to have by me simply changing the bbox_to_anchor argument from the axs[1].legend() command.

Now it reads: bbox_to_anchor=(-0.1,1) and it produces the below. Of course, you can change the first value to -0.15 or so if you want it to be more to the left.

Full code:

import numpy as np
import matplotlib.pyplot as plt

# Data
x = np.arange(0, 4 * np.pi ,0.1)
y = np.sin(x)

fig, axs = plt.subplots(1, 2, figsize=(8, 4))

# Working fine without legend title
axs[0].plot(x, y, label='sin')
axs[0].legend(title='', loc='lower left', bbox_to_anchor=(0,1), facecolor='white', edgecolor='white', framealpha=1)

# Position shifts when using long legend title
axs[1].plot(x, y, label='sin')
axs[1].legend(title='Some longer title', loc='lower left', bbox_to_anchor=(-0.1,1), facecolor='white', edgecolor='white', framealpha=1)

plt.show()

Answer 2

I found a workaround in a still unresolved issue on GitHub . Apparently the default alignment is "center", which can be changed like this.

axs[1].get_legend()._legend_box.align = "left"