Evans test

A mockup “Foo” units class which supports conversion and different tick formatting depending on the “unit”. Here the “unit” is just a scalar conversion factor, but this example shows mpl is entirely agnostic to what kind of units client packages use.

from matplotlib.cbook import iterable
import matplotlib.units as units
import matplotlib.ticker as ticker
import matplotlib.pyplot as plt


class Foo(object):
    def __init__(self, val, unit=1.0):
        self.unit = unit
        self._val = val * unit

    def value(self, unit):
        if unit is None:
            unit = self.unit
        return self._val / unit


class FooConverter(object):
    @staticmethod
    def axisinfo(unit, axis):
        'return the Foo AxisInfo'
        if unit == 1.0 or unit == 2.0:
            return units.AxisInfo(
                majloc=ticker.IndexLocator(8, 0),
                majfmt=ticker.FormatStrFormatter("VAL: %s"),
                label='foo',
                )

        else:
            return None

    @staticmethod
    def convert(obj, unit, axis):
        """
        convert obj using unit.  If obj is a sequence, return the
        converted sequence
        """
        if units.ConversionInterface.is_numlike(obj):
            return obj

        if iterable(obj):
            return [o.value(unit) for o in obj]
        else:
            return obj.value(unit)

    @staticmethod
    def default_units(x, axis):
        'return the default unit for x or None'
        if iterable(x):
            for thisx in x:
                return thisx.unit
        else:
            return x.unit


units.registry[Foo] = FooConverter()

# create some Foos
x = []
for val in range(0, 50, 2):
    x.append(Foo(val, 1.0))

# and some arbitrary y data
y = [i for i in range(len(x))]


# plot specifying units
fig = plt.figure()
fig.suptitle("Custom units")
fig.subplots_adjust(bottom=0.2)
ax = fig.add_subplot(1, 2, 2)
ax.plot(x, y, 'o', xunits=2.0)
for label in ax.get_xticklabels():
    label.set_rotation(30)
    label.set_ha('right')
ax.set_title("xunits = 2.0")


# plot without specifying units; will use the None branch for axisinfo
ax = fig.add_subplot(1, 2, 1)
ax.plot(x, y)  # uses default units
ax.set_title('default units')
for label in ax.get_xticklabels():
    label.set_rotation(30)
    label.set_ha('right')

plt.show()