Format primary and secondary y-axis values on pyplot

Question

I am having a hard time formatting a plot with a secondary axis. I would like to change the font size of the values on my primary and secondary y-axes. I have tried variations of 'set_ticks...', or 'yticks' but no luck. Can someone please give me a hand? Thanks a lot

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.ticker import FormatStrFormatter

plt.rcParams["figure.figsize"] = [16, 9]
plt.rcParams["figure.autolayout"] = True

x = [0,1,2,3,4,5,6,7,8,9,10]
y1 = [0,1,2,3,4,5,6,7,8,9,10]
y2 = [1000,900,800,700,600,500,400,300,200,100,0]

fig, ax1 = plt.subplots()

ax2 = ax1.twinx()
ax1.plot(x, y1, 'g-')
ax2.plot(x, y2, 'b-')

ax1.set_xlabel('increment', size=14)

ax1.set_ylabel('series 1', color='g', fontsize=14)
ax2.set_ylabel('series 2', color='b', size=14)

plt.title("This Plot is a Test\n\n", size=18, color='green')
plt.suptitle("\n\nJust a Test", size=18, color='blue')

ax1.yaxis.set_major_formatter(FormatStrFormatter('%.2f'))
ax1.yaxis.set_ticks(y1, size=20)

plt.grid()
plt.show();

Answer 1

There appear to be many approaches to this (welcome to matplotlib, also be aware some of the argument name capitalisations there are out of date).

Edit: My original answer seems to reset the number formatting, leaving it for comparison below this. Use ax1.tick_params(axis='y', labelsize=20).

Original answer:

The option I got working was to appending the line ax1.set_yticklabels(y1, fontsize=20) after ax1.yaxis.set_ticks(y1).

It throws a Warning if you remove the existing set_ticks line, though visually the result is the same.