219 lines
8.6 KiB
Python
219 lines
8.6 KiB
Python
# Needed ctypes routines
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from ctypes import c_double, byref
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# Other GDAL imports.
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from django.contrib.gis.gdal.base import GDALBase
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from django.contrib.gis.gdal.envelope import Envelope, OGREnvelope
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from django.contrib.gis.gdal.error import OGRException, OGRIndexError, SRSException
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from django.contrib.gis.gdal.feature import Feature
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from django.contrib.gis.gdal.field import OGRFieldTypes
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from django.contrib.gis.gdal.geomtype import OGRGeomType
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from django.contrib.gis.gdal.geometries import OGRGeometry
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from django.contrib.gis.gdal.srs import SpatialReference
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# GDAL ctypes function prototypes.
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from django.contrib.gis.gdal.prototypes import ds as capi, geom as geom_api, srs as srs_api
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from django.utils.encoding import force_bytes, force_text
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from django.utils import six
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from django.utils.six.moves import xrange
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# For more information, see the OGR C API source code:
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# http://www.gdal.org/ogr/ogr__api_8h.html
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#
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# The OGR_L_* routines are relevant here.
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class Layer(GDALBase):
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"A class that wraps an OGR Layer, needs to be instantiated from a DataSource object."
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#### Python 'magic' routines ####
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def __init__(self, layer_ptr, ds):
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"""
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Initializes on an OGR C pointer to the Layer and the `DataSource` object
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that owns this layer. The `DataSource` object is required so that a
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reference to it is kept with this Layer. This prevents garbage
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collection of the `DataSource` while this Layer is still active.
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"""
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if not layer_ptr:
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raise OGRException('Cannot create Layer, invalid pointer given')
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self.ptr = layer_ptr
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self._ds = ds
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self._ldefn = capi.get_layer_defn(self._ptr)
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# Does the Layer support random reading?
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self._random_read = self.test_capability(b'RandomRead')
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def __getitem__(self, index):
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"Gets the Feature at the specified index."
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if isinstance(index, six.integer_types):
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# An integer index was given -- we cannot do a check based on the
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# number of features because the beginning and ending feature IDs
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# are not guaranteed to be 0 and len(layer)-1, respectively.
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if index < 0: raise OGRIndexError('Negative indices are not allowed on OGR Layers.')
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return self._make_feature(index)
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elif isinstance(index, slice):
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# A slice was given
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start, stop, stride = index.indices(self.num_feat)
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return [self._make_feature(fid) for fid in xrange(start, stop, stride)]
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else:
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raise TypeError('Integers and slices may only be used when indexing OGR Layers.')
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def __iter__(self):
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"Iterates over each Feature in the Layer."
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# ResetReading() must be called before iteration is to begin.
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capi.reset_reading(self._ptr)
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for i in xrange(self.num_feat):
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yield Feature(capi.get_next_feature(self._ptr), self)
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def __len__(self):
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"The length is the number of features."
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return self.num_feat
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def __str__(self):
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"The string name of the layer."
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return self.name
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def _make_feature(self, feat_id):
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"""
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Helper routine for __getitem__ that constructs a Feature from the given
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Feature ID. If the OGR Layer does not support random-access reading,
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then each feature of the layer will be incremented through until the
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a Feature is found matching the given feature ID.
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"""
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if self._random_read:
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# If the Layer supports random reading, return.
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try:
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return Feature(capi.get_feature(self.ptr, feat_id), self)
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except OGRException:
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pass
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else:
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# Random access isn't supported, have to increment through
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# each feature until the given feature ID is encountered.
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for feat in self:
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if feat.fid == feat_id: return feat
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# Should have returned a Feature, raise an OGRIndexError.
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raise OGRIndexError('Invalid feature id: %s.' % feat_id)
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#### Layer properties ####
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@property
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def extent(self):
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"Returns the extent (an Envelope) of this layer."
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env = OGREnvelope()
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capi.get_extent(self.ptr, byref(env), 1)
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return Envelope(env)
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@property
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def name(self):
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"Returns the name of this layer in the Data Source."
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name = capi.get_fd_name(self._ldefn)
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return force_text(name, self._ds.encoding, strings_only=True)
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@property
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def num_feat(self, force=1):
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"Returns the number of features in the Layer."
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return capi.get_feature_count(self.ptr, force)
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@property
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def num_fields(self):
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"Returns the number of fields in the Layer."
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return capi.get_field_count(self._ldefn)
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@property
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def geom_type(self):
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"Returns the geometry type (OGRGeomType) of the Layer."
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return OGRGeomType(capi.get_fd_geom_type(self._ldefn))
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@property
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def srs(self):
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"Returns the Spatial Reference used in this Layer."
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try:
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ptr = capi.get_layer_srs(self.ptr)
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return SpatialReference(srs_api.clone_srs(ptr))
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except SRSException:
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return None
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@property
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def fields(self):
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"""
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Returns a list of string names corresponding to each of the Fields
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available in this Layer.
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"""
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return [force_text(capi.get_field_name(capi.get_field_defn(self._ldefn, i)),
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self._ds.encoding, strings_only=True)
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for i in xrange(self.num_fields)]
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@property
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def field_types(self):
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"""
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Returns a list of the types of fields in this Layer. For example,
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the list [OFTInteger, OFTReal, OFTString] would be returned for
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an OGR layer that had an integer, a floating-point, and string
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fields.
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"""
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return [OGRFieldTypes[capi.get_field_type(capi.get_field_defn(self._ldefn, i))]
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for i in xrange(self.num_fields)]
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@property
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def field_widths(self):
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"Returns a list of the maximum field widths for the features."
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return [capi.get_field_width(capi.get_field_defn(self._ldefn, i))
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for i in xrange(self.num_fields)]
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@property
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def field_precisions(self):
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"Returns the field precisions for the features."
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return [capi.get_field_precision(capi.get_field_defn(self._ldefn, i))
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for i in xrange(self.num_fields)]
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def _get_spatial_filter(self):
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try:
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return OGRGeometry(geom_api.clone_geom(capi.get_spatial_filter(self.ptr)))
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except OGRException:
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return None
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def _set_spatial_filter(self, filter):
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if isinstance(filter, OGRGeometry):
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capi.set_spatial_filter(self.ptr, filter.ptr)
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elif isinstance(filter, (tuple, list)):
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if not len(filter) == 4:
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raise ValueError('Spatial filter list/tuple must have 4 elements.')
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# Map c_double onto params -- if a bad type is passed in it
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# will be caught here.
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xmin, ymin, xmax, ymax = map(c_double, filter)
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capi.set_spatial_filter_rect(self.ptr, xmin, ymin, xmax, ymax)
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elif filter is None:
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capi.set_spatial_filter(self.ptr, None)
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else:
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raise TypeError('Spatial filter must be either an OGRGeometry instance, a 4-tuple, or None.')
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spatial_filter = property(_get_spatial_filter, _set_spatial_filter)
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#### Layer Methods ####
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def get_fields(self, field_name):
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"""
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Returns a list containing the given field name for every Feature
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in the Layer.
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"""
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if not field_name in self.fields:
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raise OGRException('invalid field name: %s' % field_name)
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return [feat.get(field_name) for feat in self]
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def get_geoms(self, geos=False):
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"""
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Returns a list containing the OGRGeometry for every Feature in
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the Layer.
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"""
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if geos:
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from django.contrib.gis.geos import GEOSGeometry
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return [GEOSGeometry(feat.geom.wkb) for feat in self]
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else:
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return [feat.geom for feat in self]
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def test_capability(self, capability):
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"""
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Returns a bool indicating whether the this Layer supports the given
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capability (a string). Valid capability strings include:
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'RandomRead', 'SequentialWrite', 'RandomWrite', 'FastSpatialFilter',
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'FastFeatureCount', 'FastGetExtent', 'CreateField', 'Transactions',
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'DeleteFeature', and 'FastSetNextByIndex'.
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"""
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return bool(capi.test_capability(self.ptr, force_bytes(capability)))
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