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I have the following code to plot the contents of a dataframe.

Using pandas and matplotlib:

thedata = '2013':[0.0,0.0]
 ,'2014':[0.0,0.0]
 ,'2015':[0.0,0.0]
 ,'2016':[1,0.0]
 ,'2017':[0.0,0.0]
 ,'2018':[1,0.0]

my_df = pd.DataFrame(thedata, index=['Green cars','Red cars'])

 plt.figure(figsize=(7,3))
 my_ax = plt.gca()
 my_ax.clear()
 my_ax.yaxis.set_major_locator(MaxNLocator(integer=True))

 my_df.transpose().plot(kind='bar'
 , stacked=True 
 , ax=my_ax
 ).grid(True,'major','y')

 my_ax.legend(loc=9, bbox_to_anchor=(0.5, -0.1), frameon=False, ncol=2, fontsize=12 )
 plt.title('All the cars', fontsize = 12 )
 my_ax.set_xticklabels(my_ax.get_xticklabels(),rotation='horizontal', fontsize=12)
# my_ax.set_yticklabels(my_ax.get_yticklabels(),fontsize=12)

The last line is commented out in order to get the output displayed. I want to increase the font size of the y axis labels to be the same as the x, but when i un-comment that line and run it, the y axis labels just disappear and nothing is displayed there.

Why is this happening and how do I fix it?

Edit: - create the dataframe; pandas 0.23.0, matplotlib 2.2.2

The problem you face here is that the ticklabels are not actually defined before the figure is drawn.

import matplotlib.pyplot as plt
from matplotlib.ticker import MaxNLocator

fig, ax = plt.subplots()
ax.plot([1,3,4,2])
ax.xaxis.set_major_locator(MaxNLocator(integer=True))
ax.set_xticklabels(ax.get_xticklabels(),fontsize=12)
plt.show()

You may draw the figure, before accessing those labels

fig, ax = plt.subplots()
ax.plot([1,3,4,2])
ax.xaxis.set_major_locator(MaxNLocator(integer=True))

fig.canvas.draw()
ax.set_xticklabels(ax.get_xticklabels(),fontsize=12)
plt.show()

However, in order to change the fontsize of the ticklabels, one would rather use

ax.tick_params(axis="x", labelsize=12)

or set the property to the labels, without actually setting the labels' content. E.g. via setp

plt.setp(ax.get_xticklabels(), fontsize=12)