matplotlib twinx() 2nd axis markers on the same left axis

Question

Say I create a secondary y-axis with twinx() similar to this demo

Is there a way I can place the tick marks and values of the secondary y-axis on the left side immediately next to the existing y-axis such as below ?

Answer 1

With the most recent versions of Matplotlib, this is pretty straightforward.

def add_twin(ax, **kwargs):
    twin = ax.twinx()
    twin.yaxis.tick_left()
    twin.tick_params(axis='y', direction='in', **kwargs)
    for tick in twin.get_yticklabels():
        tick.set_horizontalalignment('right')
    return twin


fig, ax = plt.subplots()
twin = add_twin(ax)
twin.set_yticks((0.1, 0.5, 0.9))

The horizontal alignment part is key, and you'll probably need to tweak the pad for your purposes, using the kwargs. But you should get something like this: