Python matplotlib restrict to integer tick locations

Question

Quite often I want to make a bar chart of counts. If the counts are low I often get major and/or minor tick locations that are not integers. How can I prevent this? It makes no sense to have a tick at 1.5 when the data are counts.

This is my first attempt:

import pylab
pylab.figure()
ax = pylab.subplot(2, 2, 1)
pylab.bar(range(1,4), range(1,4), align='center')
major_tick_locs = ax.yaxis.get_majorticklocs()
if len(major_tick_locs) < 2 or major_tick_locs[1] - major_tick_locs[0] < 1:
    ax.yaxis.set_major_locator(pylab.MultipleLocator(1))
minor_tick_locs = ax.yaxis.get_minorticklocs()
if len(minor_tick_locs) < 2 or minor_tick_locs[1] - minor_tick_locs[0] < 1:
    ax.yaxis.set_minor_locator(pylab.MultipleLocator(1))

which works OK when the counts are small but when they are large, I get many many minor ticks:

import pylab
ax = pylab.subplot(2, 2, 2)
pylab.bar(range(1,4), range(100,400,100), align='center')
major_tick_locs = ax.yaxis.get_majorticklocs()
if len(major_tick_locs) < 2 or major_tick_locs[1] - major_tick_locs[0] < 1:
    ax.yaxis.set_major_locator(pylab.MultipleLocator(1))
minor_tick_locs = ax.yaxis.get_minorticklocs()
if len(minor_tick_locs) < 2 or minor_tick_locs[1] - minor_tick_locs[0] < 1:
    ax.yaxis.set_minor_locator(pylab.MultipleLocator(1))

How can I get the desired behaviour from the first example with small counts whilst avoiding what happens in the second?

Answer 1

You can use the MaxNLocator method, like so:

    from pylab import MaxNLocator

    ya = axes.get_yaxis()
    ya.set_major_locator(MaxNLocator(integer=True))