How to set labels in matplotlib.hlines

Question

I'm trying to put labels for each line in matplotlib.hlines:

from matplotlib import pyplot as plt
plt.hlines(y=1, xmin=1, xmax=4, label='somelabel1')
plt.hlines(y=2, xmin=2, xmax=5, label='somelabel2')

I need a plot with two horizintal lines with labels on 'y' axis for each line. Instead of it I get a plot without labels, with only coordinates (see the sample image). Is it possible to put lables for each line into the plot?

Answer 1

The label kwarg is to specify the string that's displayed in a legend, not necessarily on the line itself. If you want the label to appear in your plot, you'll want to use a text object instead

plt.hlines(y=1, xmin=1, xmax=4)
plt.text(4, 1, ' somelabel1', ha='left', va='center')

plt.hlines(y=2, xmin=2, xmax=5)
plt.text(2, 2, 'somelabel2 ', ha='right', va='center')

If you instead want special y axis labels for these, you can use a custom formatter.

import matplotlib.pyplot as plt
import matplotlib.ticker as ticker

plt.hlines(y=1, xmin=1, xmax=4)
plt.hlines(y=2, xmin=2, xmax=5)

def formatter(y, pos):
    if y == 1:
        return 'label1'
    elif y == 2:
        return 'label2'
    else:
        return y

plt.gca().yaxis.set_major_formatter(ticker.FuncFormatter(formatter))