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"""
The GeometryProxy object, allows for lazy-geometries. The proxy uses
Python descriptors for instantiating and setting Geometry objects
corresponding to geographic model fields.
Thanks to Robert Coup for providing this functionality (see #4322).
"""
from types import NoneType, StringType, UnicodeType
class GeometryProxy(object):
def __init__(self, klass, field):
"""
Proxy initializes on the given Geometry class (not an instance) and
the GeometryField.
"""
self._field = field
self._klass = klass
def __get__(self, obj, type=None):
"""
This accessor retrieves the geometry, initializing it using the geometry
class specified during initialization and the HEXEWKB value of the field.
Currently, only GEOS or OGR geometries are supported.
"""
# Getting the value of the field.
geom_value = obj.__dict__[self._field.attname]
if isinstance(geom_value, self._klass):
geom = geom_value
elif (geom_value is None) or (geom_value==''):
geom = None
else:
# Otherwise, a Geometry object is built using the field's contents,
# and the model's corresponding attribute is set.
geom = self._klass(geom_value)
setattr(obj, self._field.attname, geom)
return geom
def __set__(self, obj, value):
"""
This accessor sets the proxied geometry with the geometry class
specified during initialization. Values of None, HEXEWKB, or WKT may
be used to set the geometry as well.
"""
# The OGC Geometry type of the field.
gtype = self._field._geom
# The geometry type must match that of the field -- unless the
# general GeometryField is used.
if isinstance(value, self._klass) and (str(value.geom_type).upper() == gtype or gtype == 'GEOMETRY'):
# Assigning the SRID to the geometry.
if value.srid is None: value.srid = self._field._srid
elif isinstance(value, (NoneType, StringType, UnicodeType)):
# Set with None, WKT, or HEX
pass
else:
raise TypeError('cannot set %s GeometryProxy with value of type: %s' % (obj.__class__.__name__, type(value)))
# Setting the objects dictionary with the value, and returning.
obj.__dict__[self._field.attname] = value
return value
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