Add __nonzero__ and __bool__ methods to QgsGeometry

Author: nyalldawson

doc/api_break.dox

@@ -220,8 +220,8 @@ attributeIndexes(), pkAttributeIndexes(), isSaveAndLoadStyleToDBSupported()</li>
 <li>The setGeometry( QgsGeometry* ) method has been removed, use setGeometry( const QgsGeometry& ) instead.</li>
 <li>The geometry() method now returns a copy of the geometry, not a pointer. Since QgsGeometry objects are
 implicitly shared this is a low-cost copy, and avoids ownership and dangling pointer issues. <b>Very important: Testing that
-a feature has a geometry is now done using the new hasGeometry() method. QgsFeature::geometry() will ALWAYS return
-true, as the method will return an empty geometry if the feature has no geometry.</b></li>
+a feature has a geometry is now done using the new hasGeometry() method. Any code which compares QgsFeature::geometry() to 
+None will need to be modified, as the method will return an empty geometry if the feature has no geometry.</b></li>
 <li>The temporary constGeometry() method has been removed. Use geometry() instead.</li>
 <li>setFields( const QgsFields*, bool ) has been removed, use setFields( const QgsFields&, bool ) instead.</li>
 </ul>
@@ -230,7 +230,9 @@ true, as the method will return an empty geometry if the feature has no geometry
 
 <ul>
 <li>All QgsGeometry methods now accept geometry references instead of pointers, and return a QgsGeometry
-value instead of a pointer.</li>
+value instead of a pointer. The biggest impact with this change is that PyQGIS code should not compare a geometry
+result to None, but instead either use a boolean test (`if g.buffer(10):`) or explicitly use the isEmpty()
+method to determine if a geometry is valid.</li>
 </ul>
 
 \subsection qgis_api_break_3_0_QgsGeometryAnalyzer QgsGeometryAnalyzer

python/core/__init__.py

@@ -29,6 +29,14 @@
 import string
 from qgis._core import *
 
+# Boolean evaluation of QgsGeometry
+
+
+def _geometryNonZero(self):
+    return not self.isEmpty()
+QgsGeometry.__nonzero__ = _geometryNonZero
+QgsGeometry.__bool__ = _geometryNonZero
+
 
 def register_function(function, arg_count, group, usesgeometry=False, referenced_columns=[QgsFeatureRequest.AllAttributes], **kwargs):
     """

python/plugins/processing/algs/qgis/Eliminate.py

@@ -258,7 +258,7 @@ def processAlgorithm(self, progress):
                         # We have a candidate
                         iGeom = geom2Eliminate.intersection(selGeom)
 
-                        if iGeom is None:
+                        if not iGeom:
                             continue
 
                         if boundary:

python/plugins/processing/algs/qgis/ReverseLineDirection.py

@@ -68,7 +68,7 @@ def processAlgorithm(self, progress):
             outGeom = None
             if not inGeom.isEmpty():
                 reversedLine = inGeom.geometry().reversed()
-                if reversedLine is None:
+                if not reversedLine:
                     raise GeoAlgorithmExecutionException(
                         self.tr('Error reversing line'))
                 outGeom = QgsGeometry(reversedLine)

python/plugins/processing/algs/qgis/Smooth.py

@@ -75,7 +75,7 @@ def processAlgorithm(self, progress):
             attrs = inFeat.attributes()
 
             outGeom = inGeom.smooth(iterations, offset)
-            if outGeom is None:
+            if not outGeom:
                 raise GeoAlgorithmExecutionException(
                     self.tr('Error smoothing geometry'))
 

python/plugins/processing/algs/qgis/Union.py

@@ -117,7 +117,7 @@ def processAlgorithm(self, progress):
                         int_geom = geom.intersection(tmpGeom)
                         lstIntersectingB.append(tmpGeom)
 
-                        if int_geom is None:
+                        if not int_geom:
                             # There was a problem creating the intersection
                             ProcessingLog.addToLog(ProcessingLog.LOG_INFO,
                                                    self.tr('GEOS geoprocessing error: One or more input features have invalid geometry.'))

tests/src/gui/testqgsrubberband.cpp

@@ -123,8 +123,8 @@ void TestQgsRubberband::testBoundingRect()
 
   // Polygon extent is 10,10 to 30,30
   QgsGeometry geom( QgsGeometry::fromWkt(
-                                      "POLYGON((10 10,10 30,30 30,30 10,10 10))"
-                                    ) );
+                      "POLYGON((10 10,10 30,30 30,30 10,10 10))"
+                    ) );
   mRubberband = new QgsRubberBand( mCanvas, mPolygonLayer->geometryType() );
   mRubberband->setIconSize( 5 ); // default, but better be explicit
   mRubberband->setWidth( 1 );    // default, but better be explicit
@@ -173,8 +173,8 @@ void TestQgsRubberband::testVisibility()
 
   // Check visibility after setting to valid geometry
   QgsGeometry geom( QgsGeometry::fromWkt(
-                                      "POLYGON((10 10,10 30,30 30,30 10,10 10))"
-                                    ) );
+                      "POLYGON((10 10,10 30,30 30,30 10,10 10))"
+                    ) );
   mRubberband->setToGeometry( geom, mPolygonLayer );
   QCOMPARE( mRubberband->isVisible(), true );
 

tests/src/python/test_qgsgeometry.py

@@ -58,6 +58,16 @@
 
 class TestQgsGeometry(unittest.TestCase):
 
+    def testBool(self):
+        """ Test boolean evaluation of QgsGeometry """
+        g = QgsGeometry()
+        self.assertFalse(g)
+        myWKT = 'Point (10 10)'
+        g = QgsGeometry.fromWkt(myWKT)
+        self.assertTrue(g)
+        g.setGeometry(None)
+        self.assertFalse(g)
+
     def testWktPointLoading(self):
         myWKT = 'Point (10 10)'
         myGeometry = QgsGeometry.fromWkt(myWKT)
@@ -1516,7 +1526,7 @@ def testConvertToType(self):
         ######## TO LINE ########
         # POINT TO LINE
         point = QgsGeometry.fromPoint(QgsPoint(1, 1))
-        assert point.convertToType(Qgis.Line, False) is None, "convertToType with a point should return a null geometry"
+        self.assertFalse(point.convertToType(Qgis.Line, False)), "convertToType with a point should return a null geometry"
         # MultiPoint TO LINE
         multipoint = QgsGeometry.fromMultiPoint(points[0][0])
         wkt = multipoint.convertToType(Qgis.Line, False).exportToWkt()
@@ -1581,10 +1591,10 @@ def testConvertToType(self):
         assert compareWkt(expWkt, wkt), "convertToType failed: from line to polygon. Expected:\n%s\nGot:\n%s\n" % (expWkt, wkt)
         # LINE ( 3 vertices, with first = last ) TO Polygon
         line = QgsGeometry.fromPolyline([QgsPoint(1, 1), QgsPoint(0, 0), QgsPoint(1, 1)])
-        assert line.convertToType(Qgis.Polygon, False) is None, "convertToType to polygon of a 3 vertices lines with first and last vertex identical should return a null geometry"
+        self.assertFalse(line.convertToType(Qgis.Polygon, False), "convertToType to polygon of a 3 vertices lines with first and last vertex identical should return a null geometry")
         # MULTILINE ( with a part of 3 vertices, with first = last ) TO MultiPolygon
         multiline = QgsGeometry.fromMultiPolyline([points[0][0], [QgsPoint(1, 1), QgsPoint(0, 0), QgsPoint(1, 1)]])
-        assert multiline.convertToType(Qgis.Polygon, True) is None, "convertToType to polygon of a 3 vertices lines with first and last vertex identical should return a null geometry"
+        self.assertFalse(multiline.convertToType(Qgis.Polygon, True), "convertToType to polygon of a 3 vertices lines with first and last vertex identical should return a null geometry")
         # LINE TO MultiPolygon
         line = QgsGeometry.fromPolyline(points[0][0])
         wkt = line.convertToType(Qgis.Polygon, True).exportToWkt()