[FEATURE][API] Add some nice PyQGIS API for working with geometry col…

…lections

- Calling removeGeometry with an invalid index will now raise an IndexError
- Calling collection[0] will return the first geometry in the collection,
collection[1] the second, etc. And negative indices return from the end
of the collection, so collection[-1] returns the last geometry in the collection.
- Geometries can be deleted by calling `del collection[1]` (deletes the
second geometry from the collection). Also supports negative indices
to count from the end of the collection.

python/core/auto_generated/geometry/qgsgeometrycollection.sip.in

@@ -109,13 +109,26 @@ Inserts a geometry before a specified index and takes ownership. Returns true in
 :param index: position to insert geometry before
 %End
 
+
     virtual bool removeGeometry( int nr );
 %Docstring
-Removes a geometry from the collection.
+Removes a geometry from the collection by index.
 
-:param nr: index of geometry to remove
+An IndexError will be raised if no geometry with the specified index exists.
 
 :return: true if removal was successful.
+%End
+%MethodCode
+    const int count = sipCpp->numGeometries();
+    if ( a0 < 0 || a0 >= count )
+    {
+      PyErr_SetString( PyExc_IndexError, QByteArray::number( a0 ) );
+      sipIsErr = 1;
+    }
+    else
+    {
+      sipCpp->removeGeometry( a0 );
+    }
 %End
 
     virtual void transform( const QgsCoordinateTransform &ct, QgsCoordinateTransform::TransformDirection d = QgsCoordinateTransform::ForwardTransform, bool transformZ = false ) throw( QgsCsException );
@@ -207,6 +220,56 @@ Returns a geometry without curves. Caller takes ownership
 
 
 
+
+
+    SIP_PYOBJECT __getitem__( int index );
+%Docstring
+Returns the geometry at the specified ``index``. An IndexError will be raised if no geometry with the specified ``index`` exists.
+
+Indexes can be less than 0, in which case they correspond to geometries from the end of the collect. E.g. an index of -1
+corresponds to the last geometry in the collection.
+
+.. versionadded:: 3.6
+%End
+%MethodCode
+    const int count = sipCpp->numGeometries();
+    if ( a0 < -count || a0 >= count )
+    {
+      PyErr_SetString( PyExc_IndexError, QByteArray::number( a0 ) );
+      sipIsErr = 1;
+    }
+    else if ( a0 >= 0 )
+    {
+      return sipConvertFromType( sipCpp->geometryN( a0 ), sipType_QgsAbstractGeometry, NULL );
+    }
+    else
+    {
+      return sipConvertFromType( sipCpp->geometryN( count + a0 ), sipType_QgsAbstractGeometry, NULL );
+    }
+%End
+
+    void __delitem__( int index );
+%Docstring
+Deletes the geometry at the specified ``index``. A geometry at the ``index`` must already exist or an IndexError will be raised.
+
+Indexes can be less than 0, in which case they correspond to geometries from the end of the collection. E.g. an index of -1
+corresponds to the last geometry in the collection.
+
+.. versionadded:: 3.6
+%End
+%MethodCode
+    const int count = sipCpp->numGeometries();
+    if ( a0 >= 0 && a0 < count )
+      sipCpp->removeGeometry( a0 );
+    else if ( a0 < 0 && a0 >= -count )
+      sipCpp->removeGeometry( count + a0 );
+    else
+    {
+      PyErr_SetString( PyExc_IndexError, QByteArray::number( a0 ) );
+      sipIsErr = 1;
+    }
+%End
+
     virtual QgsGeometryCollection *createEmptyWithSameType() const /Factory/;
 
 

src/core/geometry/qgsgeometrycollection.h

@@ -124,12 +124,37 @@ class CORE_EXPORT QgsGeometryCollection: public QgsAbstractGeometry
      */
     virtual bool insertGeometry( QgsAbstractGeometry *g SIP_TRANSFER, int index );
 
+#ifndef SIP_RUN
+
     /**
      * Removes a geometry from the collection.
      * \param nr index of geometry to remove
      * \returns true if removal was successful.
      */
     virtual bool removeGeometry( int nr );
+#else
+
+    /**
+     * Removes a geometry from the collection by index.
+     *
+     * An IndexError will be raised if no geometry with the specified index exists.
+     *
+     * \returns true if removal was successful.
+     */
+    virtual bool removeGeometry( int nr );
+    % MethodCode
+    const int count = sipCpp->numGeometries();
+    if ( a0 < 0 || a0 >= count )
+    {
+      PyErr_SetString( PyExc_IndexError, QByteArray::number( a0 ) );
+      sipIsErr = 1;
+    }
+    else
+    {
+      sipCpp->removeGeometry( a0 );
+    }
+    % End
+#endif
 
     void transform( const QgsCoordinateTransform &ct, QgsCoordinateTransform::TransformDirection d = QgsCoordinateTransform::ForwardTransform, bool transformZ = false ) override SIP_THROW( QgsCsException );
     void transform( const QTransform &t, double zTranslate = 0.0, double zScale = 1.0, double mTranslate = 0.0, double mScale = 1.0 ) override;
@@ -202,6 +227,58 @@ class CORE_EXPORT QgsGeometryCollection: public QgsAbstractGeometry
     }
 #endif
 
+
+#ifdef SIP_RUN
+
+    /**
+    * Returns the geometry at the specified ``index``. An IndexError will be raised if no geometry with the specified ``index`` exists.
+    *
+    * Indexes can be less than 0, in which case they correspond to geometries from the end of the collect. E.g. an index of -1
+    * corresponds to the last geometry in the collection.
+    *
+    * \since QGIS 3.6
+    */
+    SIP_PYOBJECT __getitem__( int index );
+    % MethodCode
+    const int count = sipCpp->numGeometries();
+    if ( a0 < -count || a0 >= count )
+    {
+      PyErr_SetString( PyExc_IndexError, QByteArray::number( a0 ) );
+      sipIsErr = 1;
+    }
+    else if ( a0 >= 0 )
+    {
+      return sipConvertFromType( sipCpp->geometryN( a0 ), sipType_QgsAbstractGeometry, NULL );
+    }
+    else
+    {
+      return sipConvertFromType( sipCpp->geometryN( count + a0 ), sipType_QgsAbstractGeometry, NULL );
+    }
+    % End
+
+    /**
+     * Deletes the geometry at the specified ``index``. A geometry at the ``index`` must already exist or an IndexError will be raised.
+     *
+     * Indexes can be less than 0, in which case they correspond to geometries from the end of the collection. E.g. an index of -1
+     * corresponds to the last geometry in the collection.
+     *
+     * \since QGIS 3.6
+     */
+    void __delitem__( int index );
+    % MethodCode
+    const int count = sipCpp->numGeometries();
+    if ( a0 >= 0 && a0 < count )
+      sipCpp->removeGeometry( a0 );
+    else if ( a0 < 0 && a0 >= -count )
+      sipCpp->removeGeometry( count + a0 );
+    else
+    {
+      PyErr_SetString( PyExc_IndexError, QByteArray::number( a0 ) );
+      sipIsErr = 1;
+    }
+    % End
+#endif
+
     QgsGeometryCollection *createEmptyWithSameType() const override SIP_FACTORY;
 
   protected:

tests/src/python/test_qgsgeometry.py

@@ -433,6 +433,71 @@ def testLineStringPythonAdditions(self):
         with self.assertRaises(IndexError):
             del ls[-3]
 
+    def testGeometryCollectionPythonAdditions(self):
+        """
+        Tests Python specific additions to the QgsGeometryCollection API
+        """
+        g = QgsGeometryCollection()
+        self.assertTrue(bool(g))
+        self.assertEqual(len(g), 0)
+        g = QgsGeometryCollection()
+        g.fromWkt('GeometryCollection( Point(1  2), Point(11 12))')
+        self.assertTrue(bool(g))
+        self.assertEqual(len(g), 2)
+
+        # pointN
+        with self.assertRaises(IndexError):
+            g.geometryN(-1)
+        with self.assertRaises(IndexError):
+            g.geometryN(2)
+        self.assertEqual(g.geometryN(0), QgsPoint(1, 2))
+        self.assertEqual(g.geometryN(1), QgsPoint(11, 12))
+
+        # removeGeometry
+        g.fromWkt('GeometryCollection( Point(1  2), Point(11 12), Point(33 34))')
+        with self.assertRaises(IndexError):
+            g.removeGeometry(-1)
+        with self.assertRaises(IndexError):
+            g.removeGeometry(3)
+        g.removeGeometry(1)
+        self.assertEqual(len(g), 2)
+        self.assertEqual(g.geometryN(0), QgsPoint(1, 2))
+        self.assertEqual(g.geometryN(1), QgsPoint(33, 34))
+        with self.assertRaises(IndexError):
+            g.removeGeometry(2)
+
+        g.fromWkt('GeometryCollection( Point(25 16 37 58), Point(26 22 47 68))')
+        # get item
+        with self.assertRaises(IndexError):
+            g[-3]
+        with self.assertRaises(IndexError):
+            g[2]
+        self.assertEqual(g[0], QgsPoint(25, 16, 37, 58))
+        self.assertEqual(g[1], QgsPoint(26, 22, 47, 68))
+        self.assertEqual(g[-2], QgsPoint(25, 16, 37, 58))
+        self.assertEqual(g[-1], QgsPoint(26, 22, 47, 68))
+
+        # del item
+        g.fromWkt('GeometryCollection( Point(1  2), Point(11 12), Point(33 34))')
+        with self.assertRaises(IndexError):
+            del g[-4]
+        with self.assertRaises(IndexError):
+            del g[3]
+        del g[1]
+        self.assertEqual(len(g), 2)
+        self.assertEqual(g[0], QgsPoint(1, 2))
+        self.assertEqual(g[1], QgsPoint(33, 34))
+        with self.assertRaises(IndexError):
+            del g[2]
+
+        g.fromWkt('GeometryCollection( Point(1  2), Point(11 12), Point(33 34))')
+        del g[-3]
+        self.assertEqual(len(g), 2)
+        self.assertEqual(g[0], QgsPoint(11, 12))
+        self.assertEqual(g[1], QgsPoint(33, 34))
+        with self.assertRaises(IndexError):
+            del g[-3]
+
     def testReferenceGeometry(self):
         """ Test parsing a whole range of valid reference wkt formats and variants, and checking
         expected values such as length, area, centroids, bounding boxes, etc of the resultant geometry.