matplotlib axis('tight') doesn't work?

Question

According to the documentation, ax.autoscale(tight=True) should

If True, set view limits to data limits;

With ax.ax

Answer 1

You're not necessarily doing anything wrong. You're using matplotlib version 2 (or greater). In this version the default plot layout was changed so that the axis had 5% padding added on to either end. Here's a link describing the plot layout: https://matplotlib.org/users/dflt_style_changes.html#plot-layout

From the link, to change it back to the 'classic' style, use:

mpl.rcParams['axes.autolimit_mode'] = 'round_numbers'
mpl.rcParams['axes.xmargin'] = 0
mpl.rcParams['axes.ymargin'] = 0

Answer 2

By setting the autoscale you should see the desired difference between tight=True and tight=False.

f, (ax, ax2) = plt.subplots(ncols=2)

ax.plot([0, 1], [1, 0], label="tight=True")
ax.autoscale(enable=True, axis='both', tight=True)

ax2.plot([0, 1], [1, 0], label="tight=False")
ax2.autoscale(enable=True, axis='both', tight=False)

ax.legend()
ax2.legend()

You may note that ax.axis("tight") is not related; it only states in the documentation that

‘tight’ Limits set such that all data is shown

which is indeed the case, all data is shown (it doesn't say anything about setting the view limits to exactly the data).