Plot two lines in one graph with each line own y-values

Question

Using Matplotlib, I would like to plot two lines in one graph, where both lines have their own axis.

Currently, I have:

x = [3, 5, 7, 9, 10, 11, 13, 15, 17, 19, 20, 21, 23, 25, 27, 30, 35, 40, 45, 50]
y1 = [0.658431,0.702574,0.727149,0.760198,0.746229,0.768321,0.763344,0.764400,0.759935,0.758930,0.769689,0.773518,0.764118,0.780918,0.767377,0.766301,0.779629,0.774025,0.773127,0.782209]
y2 = [0.008676, 0.014630, 0.021286, 0.025562, 0.018247, 0.026771, 0.036187, 0.025633, 0.031402, 0.031140, 0.031333, 0.027820, 0.020359, 0.033351, 0.032603, 0.027474, 0.025250, 0.023103, 0.030988, 0.026503]

plt.plot(x, y1, label = "line 1")
plt.plot(x, y2, label = "line 2")
  
plt.xlabel('x - axis')
plt.ylabel('y - axis')
plt.title('Y1 and Y2')
  
plt.legend()

Which results in:

However, both lines look relatively flat as they are represented on the same axis and have a different scale. Instead, I would like an y-axis on the left from 0.66 to 0.78 (to represent y1) and I would like an y-axis on the right between 0 and 0.05 (to represent y2). Then, y1's values can be read on the left axis and y2's values can be read on the right axis and the relative changes are illustrated clearer.

How can I do this?

Answer 1

Based on @rperezsoto's comment, I have the following working code:

fig, ax1 = plt.subplots()

color = 'tab:red'
ax1.set_xlabel('x-axis')
ax1.set_ylabel('AUC', color='blue')
ax1.plot(x, y1, color='blue')
ax1.tick_params(axis='y', labelcolor='blue')

ax2 = ax1.twinx()  # instantiate a second axes that shares the same x-axis

color = 'tab:blue'
ax2.set_ylabel('Standard deviation', color='grey')  # we already handled the x-label with ax1
ax2.plot(x, y2, color='grey')
ax2.tick_params(axis='y', labelcolor='grey')

fig.tight_layout()  # otherwise the right y-label is slightly clipped
plt.title('Y1 and Y2')
plt.show()