A perfect easy beautiful simple way to label a stacked bar chart in Python using pandas/matplotlib. Put this in your Jupyter notebook!

chart.py

#
# WAIT!!!
# WAIT!!!
# You probably don't need this any more! Newer versions of matplotlib
# can do this with built-in magic. See these StackOverflow answers:
#
# https://stackoverflow.com/questions/41296313/stacked-bar-chart-with-centered-labels/60895640#60895640
# https://stackoverflow.com/questions/28931224/adding-value-labels-on-a-matplotlib-bar-chart/67561982#67561982
#
# Big thanks to @trenton3983 for keeping us all up to date!
#

%matplotlib inline

import pandas as pd

df = pd.DataFrame({
    'cat': [3, 5, 4, 3, 3, 23, 4],
    'dog': [3, 23, 4, 3, 5, 4, 3],
    'mouse': [3, 23, 4, 3, 5, 4, 3]
})

# Save the chart that's drawn
ax = df.plot(stacked=True, kind='barh', figsize=(10, 5))

# .patches is everything inside of the chart, lines and
# rectangles and circles and stuff. In this case we only
# have rectangles!
for rect in ax.patches:
    # Find where everything is located
    height = rect.get_height()
    width = rect.get_width()
    x = rect.get_x()
    y = rect.get_y()
    
    # The width of the bar is also not pixels, it's the
    # number of animals. So we can use it as the label!
    label_text = width
    
    # ax.text(x, y, text)
    label_x = x + width / 2
    label_y = y + height / 2
    ax.text(label_x, label_y, label_text, ha='center', va='center')

Praise be to the matplotlib gods! Thanks a zillion for posting this, just updated the original!