content: """
  The classes here provide support for using custom classes with
  matplotlib, eg 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, eg 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 support 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):
              'convert value to a scalar or array'
              return dates.date2num(value)
          convert = staticmethod(convert)
  
          def axisinfo(unit):
              'return major and minor tick locators and formatters'
              if unit!='date': return None
              majloc = dates.AutoDateLocator()
              majfmt = dates.AutoDateFormatter(majloc)
              return AxisInfo(majloc=majloc,
                              majfmt=majfmt,
                              label='date')
          axisinfo = staticmethod(axisinfo)
  
  
          def default_units(x):
              'return the default unit for x or None'
              return 'date'
          default_units = staticmethod(default_units)
  
      # finally we register our object type with a converter
      units.registry[datetime.date] = DateConverter()
  
  """
  import numpy as np
  from matplotlib.cbook import iterable, is_numlike
  
  class AxisInfo:
      'information to support default axis labeling and tick labeling'
      def __init__(self, majloc=None, minloc=None,
                   majfmt=None, minfmt=None, label=None):
          """
          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
  
          If any of the above are None, the axis will simply use the default
          """
          self.majloc = majloc
          self.minloc = minloc
          self.majfmt = majfmt
          self.minfmt = minfmt
          self.label = label
  
  
  class ConversionInterface:
      """
      The minimal interface for a converter to take custom instances (or
      sequences) and convert them to values mpl can use
      """
      def axisinfo(unit):
          'return an units.AxisInfo instance for unit'
          return None
      axisinfo = staticmethod(axisinfo)
  
      def default_units(x):
          'return the default unit for x or None'
          return None
      default_units = staticmethod(default_units)
  
      def convert(obj, unit):
          """
          convert obj using unit.  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
          """
          return obj
      convert = staticmethod(convert)
  
      def 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.
          """
          if iterable(x):
              for thisx in x:
                  return is_numlike(thisx)
          else:
              return is_numlike(x)
      is_numlike = staticmethod(is_numlike)
  
  class Registry(dict):
      """
      register types with conversion interface
      """
      def __init__(self):
          dict.__init__(self)
          self._cached = {}
  
      def get_converter(self, x):
          'get the converter interface instance for x, or None'
  
          if not len(self): return None # nothing registered
          #DISABLED idx = id(x)
          #DISABLED cached = self._cached.get(idx)
          #DISABLED if cached is not None: return cached
  
          converter = None
          classx = getattr(x, '__class__', None)
  
          if classx is not None:
              converter = self.get(classx)
  
          if converter is None and iterable(x):
              # if this is anything but an object array, we'll assume
              # there are no custom units
              if isinstance(x, np.ndarray) and x.dtype != np.object:
                  return None
  
              for thisx in x:
                  converter = self.get_converter( thisx )
                  return converter
  
          #DISABLED self._cached[idx] = converter
          return converter
  
  
  registry = Registry()
  