How to draw grid lines behind matplotlib bar graph

To add a grid you simply need to add

ax.grid()

If you want the grid to be behind the bars then add

ax.grid(zorder=0)
ax.bar(range(len(y)), y, width=0.3, align='center', color='skyblue', zorder=3)

The important part is that the zorder of the bars is greater than grid. Experimenting it seems zorder=3 is the lowest value that actually gives the desired effect. I have no idea why zorder=1 isn't sufficient.

EDIT: I have noticed this question has already been answered here using a different method although it suffers some link rot. Both methods yield the same result as far as I can see but andrew cooke's answer is more elegant.

I am suggesting another solution since the most voted answer did not work for me. You can use the following code to set the gridlines behind the plot.

ax.set_axisbelow(True)
ax.grid(color='gray', linestyle='dashed')

I got this code from this answer.