Python / Matplotlib - 如何将文本放在相等方面图的角落

Question

I would like to put text in the right bottom corner of equal aspect figure. I set the position relative to the figure by ax.transAxes, but I have to define the relative coordinate value manually depending on height scales of each figures.

What would be a good way to know axes height scale and the correct text position within the script?

 ax = plt.subplot(2,1,1)
 ax.plot([1,2,3],[1,2,3])
 ax.set_aspect('equal')
 ax.text(1,-0.15, 'text', transform=ax.transAxes, ha='right', fontsize=16)
 print ax.get_position().height

 ax = plt.subplot(2,1,2)
 ax.plot([10,20,30],[1,2,3])
 ax.set_aspect('equal')
 ax.text(1,-0.15, 'text', transform=ax.transAxes, ha='right', fontsize=16)
 print ax.get_position().height                                              

Answer 1

Use annotate .

In fact, I hardly ever use text . Even when I want to place things in data coordinates, I usually want to offset it by some fixed distance in points, which is much easier with annotate .

As a quick example:

import matplotlib.pyplot as plt

fig, axes = plt.subplots(nrows=2, subplot_kw=dict(aspect=1))

axes[0].plot(range(1, 4))
axes[1].plot(range(10, 40, 10), range(1, 4))

for ax in axes:
    ax.annotate('Test', xy=(1, 0), xycoords='axes fraction', fontsize=16,
                horizontalalignment='right', verticalalignment='bottom')
plt.show()

If you'd like it slightly offset from the corner, you can specify an offset through the xytext kwarg (and textcoords to control how the values of xytext are interpreted). I'm also using the ha and va abbreviations for horizontalalignment and verticalalignment here:

import matplotlib.pyplot as plt

fig, axes = plt.subplots(nrows=2, subplot_kw=dict(aspect=1))

axes[0].plot(range(1, 4))
axes[1].plot(range(10, 40, 10), range(1, 4))

for ax in axes:
    ax.annotate('Test', xy=(1, 0), xycoords='axes fraction', fontsize=16,
                xytext=(-5, 5), textcoords='offset points',
                ha='right', va='bottom')
plt.show()

If you're trying to place it below the axes, you can use the offset to place it a set distance below in points:

import matplotlib.pyplot as plt

fig, axes = plt.subplots(nrows=2, subplot_kw=dict(aspect=1))

axes[0].plot(range(1, 4))
axes[1].plot(range(10, 40, 10), range(1, 4))

for ax in axes:
    ax.annotate('Test', xy=(1, 0), xycoords='axes fraction', fontsize=16,
                xytext=(0, -15), textcoords='offset points',
                ha='right', va='top')
plt.show()

Also have a look at the Matplotlib annotation guide for more information.