在matplotlib的右yaxis上添加刻度标签

Question

I have the following graph:

I'd like to add custom ticks with labels on the right hand side of the graph, to identify the dashed horizontal lines. How can I do that?

Answer 1

ax = gca()
ax.axhline(.5, linestyle='--')
trans = matplotlib.transforms.blended_transform_factory(
    ax.transAxes,
    ax.transData)

ax.annotate('label', xy=(1.01, .5), xycoords=trans, clip_on=False, va='center')
ax.set_xlim([0,2])
plt.draw()

See here for details on blended transforms. The x coordinate in is axis units (so it will always be just a tad off to the right, and the y-coordinate is is data units so you can put it exactly where you want. There isn't much point in putting in ticks on the right because you dashed lines will cover them up.

Answer 2

If you want a new scale, use twinx() .

fig = plt.figure()
ax = []
ax.append(fig.add_subplot(111))
ax.append(ax[0].twinx())
ax[0].plot(...)
ax[1].set_yticks([...])
ax[1].set_yticklabels([...])
plt.show()

If you want just a label, use a text thingy, as @tcaswell wrote.