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from ctypes import c_void_p
from types import NoneType
from django.contrib.gis.gdal.error import GDALException
class GDALBase(object):
"""
Base object for GDAL objects that has a pointer access property
that controls access to the underlying C pointer.
"""
# Initially the pointer is NULL.
_ptr = None
# Default allowed pointer type.
ptr_type = c_void_p
# Pointer access property.
def _get_ptr(self):
# Raise an exception if the pointer isn't valid don't
# want to be passing NULL pointers to routines --
# that's very bad.
if self._ptr: return self._ptr
else: raise GDALException('GDAL %s pointer no longer valid.' % self.__class__.__name__)
def _set_ptr(self, ptr):
# Only allow the pointer to be set with pointers of the
# compatible type or None (NULL).
if isinstance(ptr, (int, long)):
self._ptr = self.ptr_type(ptr)
elif isinstance(ptr, (self.ptr_type, NoneType)):
self._ptr = ptr
else:
raise TypeError('Incompatible pointer type')
ptr = property(_get_ptr, _set_ptr)
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