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The classes here provide support for using custom classes with matplotlib, e.g., those that do not expose the array interface but know how to converter themselves to arrays. It also supoprts classes with units and units conversion. Use cases include converters for custom objects, e.g., a list of datetime objects, as well as for objects that are unit aware. We don’t assume any particular units implementation, rather a units implementation must provide a ConversionInterface, and the register with the Registry converter dictionary. For example, here is a complete implementation which supports plotting with native datetime objects:

import matplotlib.units as units
import matplotlib.dates as dates
import matplotlib.ticker as ticker
import datetime

class DateConverter(units.ConversionInterface):

    def convert(value, unit, axis):
        'convert value to a scalar or array'
        return dates.date2num(value)

    def axisinfo(unit, axis):
        'return major and minor tick locators and formatters'
        if unit!='date': return None
        majloc = dates.AutoDateLocator()
        majfmt = dates.AutoDateFormatter(majloc)
        return AxisInfo(majloc=majloc,

    def default_units(x, axis):
        'return the default unit for x or None'
        return 'date'

# finally we register our object type with a converter
units.registry[] = DateConverter()
class matplotlib.units.AxisInfo(majloc=None, minloc=None, majfmt=None, minfmt=None, label=None, default_limits=None)

Bases: object

information to support default axis labeling and tick labeling, and default limits

majloc and minloc: TickLocators for the major and minor ticks majfmt and minfmt: TickFormatters for the major and minor ticks label: the default axis label default_limits: the default min, max of the axis if no data is present If any of the above are None, the axis will simply use the default

class matplotlib.units.ConversionInterface

Bases: object

The minimal interface for a converter to take custom instances (or sequences) and convert them to values mpl can use

static axisinfo(unit, axis)

return an units.AxisInfo instance for axis with the specified units

static convert(obj, unit, axis)

convert obj using unit for the specified axis. If obj is a sequence, return the converted sequence. The ouput must be a sequence of scalars that can be used by the numpy array layer

static default_units(x, axis)

return the default unit for x or None for the given axis

static is_numlike(x)

The matplotlib datalim, autoscaling, locators etc work with scalars which are the units converted to floats given the current unit. The converter may be passed these floats, or arrays of them, even when units are set. Derived conversion interfaces may opt to pass plain-ol unitless numbers through the conversion interface and this is a helper function for them.

class matplotlib.units.Registry

Bases: dict

register types with conversion interface


get the converter interface instance for x, or None