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units example code: ellipse_with_units.py

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(Source code, png, hires.png, pdf)

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:
    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:

    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"),

            return None

    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]
            return obj.value(unit)

    def default_units(x, axis):
        'return the default unit for x or None'
        if iterable(x):
            for thisx in x:
                return thisx.unit
            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")
ax = fig.add_subplot(1,2,2)
ax.plot( x, y, 'o', xunits=2.0 )
for label in ax.get_xticklabels():
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():


Keywords: python, matplotlib, pylab, example, codex (see Search examples)