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

Answer 1

 pylab.bar(range(1,4), range(1,4), align='center')  

and

 xticks(range(1,40),range(1,40))

has worked in my code. Just use the align optional parameter and xticks does the magic.

Answer 2

You can use the MaxNLocator method, like so:

    from pylab import MaxNLocator

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

Answer 3

I think it turns out I can just ignore the minor ticks. I'm going to give this a go and see if it stands up in all use cases:

def ticks_restrict_to_integer(axis):
    """Restrict the ticks on the given axis to be at least integer,
    that is no half ticks at 1.5 for example.
    """
    from matplotlib.ticker import MultipleLocator
    major_tick_locs = axis.get_majorticklocs()
    if len(major_tick_locs) < 2 or major_tick_locs[1] - major_tick_locs[0] < 1:
        axis.set_major_locator(MultipleLocator(1))

def _test_restrict_to_integer():
    pylab.figure()
    ax = pylab.subplot(1, 2, 1)
    pylab.bar(range(1,4), range(1,4), align='center')
    ticks_restrict_to_integer(ax.xaxis)
    ticks_restrict_to_integer(ax.yaxis)

    ax = pylab.subplot(1, 2, 2)
    pylab.bar(range(1,4), range(100,400,100), align='center')
    ticks_restrict_to_integer(ax.xaxis)
    ticks_restrict_to_integer(ax.yaxis)

_test_restrict_to_integer()
pylab.show()