update

code/pyqgis/processing/save_attributes_algorithm.py

@@ -1,76 +1,92 @@
-from PyQt5.QtCore import QCoreApplication
-from qgis.core import (QgsProcessing,
-                       QgsProcessingAlgorithm,
-                       QgsProcessingParameterFeatureSource,
-                       QgsProcessingParameterFileDestination)
-
-
-class SaveAttributesAlgorithm(QgsProcessingAlgorithm):
-    """Saves the attributes of a vector layer to a CSV file."""
-    OUTPUT = 'OUTPUT'
-    INPUT = 'INPUT'
-
-    def initAlgorithm(self, config=None):
-        self.addParameter(
-            QgsProcessingParameterFeatureSource(
-                self.INPUT,
-                self.tr('Input layer'),
-                [QgsProcessing.TypeVectorAnyGeometry]
-            )
-        )
-
-        # We add a file output of type CSV.
-        self.addParameter(
-            QgsProcessingParameterFileDestination(
-                self.OUTPUT,
-                self.tr('Output File'),
-                'CSV files (*.csv)',
-            )
-        )
-
-    def processAlgorithm(self, parameters, context, feedback):
-        source = self.parameterAsSource(parameters, self.INPUT, context)
-        csv = self.parameterAsFileOutput(parameters, self.OUTPUT, context)
-
-        fieldnames = [field.name() for field in source.fields()]
-
-        # Compute the number of steps to display within the progress bar and
-        # get features from source
-        total = 100.0 / source.featureCount() if source.featureCount() else 0
-        features = source.getFeatures()
-
-        with open(csv, 'w') as output_file:
-          # write header
-          line = ','.join(name for name in fieldnames) + '\n'
-          output_file.write(line)
-          for current, f in enumerate(features):
-              # Stop the algorithm if cancel button has been clicked
-              if feedback.isCanceled():
-                  break
-
-              # Add a feature in the sink
-              line = ','.join(str(f[name]) for name in fieldnames) + '\n'
-              output_file.write(line)
-
-              # Update the progress bar
-              feedback.setProgress(int(current * total))
-
-        return {self.OUTPUT: csv}
-
-    def name(self):
-        return 'save_attributes'
-
-    def displayName(self):
-        return self.tr('Save Attributes As CSV')
-
-    def group(self):
-        return self.tr(self.groupId())
-
-    def groupId(self):
-        return ''
-
-    def tr(self, string):
-        return QCoreApplication.translate('Processing', string)
-
-    def createInstance(self):
-        return SaveAttributesAlgorithm()
+from PyQt5.QtCore import QCoreApplication
+from qgis.core import (QgsProcessing,
+                       QgsProcessingAlgorithm,
+                       QgsProcessingParameterFeatureSource,
+                       QgsProcessingParameterEnum,
+                       QgsProcessingParameterFileDestination,
+                       QgsVectorFileWriter,
+                       QgsWkbTypes,
+                       QgsProject)
+
+
+class SaveAttributesAlgorithm(QgsProcessingAlgorithm):
+    """Saves the attributes of a vector layer to a CSV file."""
+
+    def initAlgorithm(self, config=None):
+        self.addParameter(
+            QgsProcessingParameterFeatureSource(
+                'INPUT',
+                'Input layer',
+                [QgsProcessing.TypeVectorAnyGeometry]
+            )
+        )
+
+        # We add a file output of type CSV.
+        self.addParameter(
+            QgsProcessingParameterFileDestination(
+                'OUTPUT',
+                'Output File',
+                'CSV files (*.csv)',
+            )
+        )
+
+    def processAlgorithm(self, parameters, context, feedback):
+        layer = self.parameterAsVectorLayer(
+            parameters,
+            'INPUT',
+            context)
+
+        output = self.parameterAsFileOutput(
+            parameters,
+            'OUTPUT',
+            context)
+
+        # Compute the number of steps to display within the progress bar and
+        # get features from source
+        total = 100.0 / layer.featureCount() if layer.featureCount() else 0
+        features = layer.getFeatures()
+
+        # Define the options for saving the layer
+        save_options = QgsVectorFileWriter.SaveVectorOptions()
+        save_options.driverName = 'CSV'
+        save_options.fileEncoding = 'UTF-8'
+
+        # Create the writer
+        writer = QgsVectorFileWriter.create(
+            fileName=output,
+            fields=layer.fields(),
+            geometryType=QgsWkbTypes.NoGeometry,
+            srs=layer.crs(),
+            transformContext=QgsProject.instance().transformContext(),
+            options=save_options)
+
+
+        for current, f in enumerate(features):
+            # Stop the algorithm if cancel button has been clicked
+            if feedback.isCanceled():
+                break
+
+            # Add a feature in the sink
+            writer.addFeature(f)
+
+            # Update the progress bar
+            feedback.setProgress(int(current * total))
+        return {'OUTPUT': output}
+
+    def name(self):
+        return 'save_attributes'
+
+    def displayName(self):
+        return self.tr('Save Attributes As CSV')
+
+    def group(self):
+        return self.tr(self.groupId())
+
+    def groupId(self):
+        return ''
+
+    def tr(self, string):
+        return QCoreApplication.translate('Processing', string)
+
+    def createInstance(self):
+        return SaveAttributesAlgorithm()

code/pyqgis/solutions/exercise8.py

@@ -1,64 +1,4 @@
-import os
-import time
-
-data_dir = os.path.join(os.path.expanduser('~'), 'Downloads', 'pyqgis_masterclass')
-
 layer = iface.activeLayer()
+field_names = [field.name() for field in layer.fields()]
 
-# Check if a layer is selected
-if not layer:
-    iface.messageBar().pushMessage('Please select a layer',  level=Qgis.Critical) 
-# Check if the selected layer is a vector layer
-if layer.type() != QgsMapLayer.VectorLayer:
-    iface.messageBar().pushMessage('Please select a vector layer',  level=Qgis.Critical)
-
-# Define parameters for QgsVectorFileWriter
-output_name = 'output.csv'
-output_path = os.path.join(data_dir, output_name)
-
-# We will use QgsVectorFileWriter.create() method
-# It takes the following parameters
-# fileName: Path to the file
-# fields: Fields to write
-# geometryType: geometry type of output file
-# srs: CRS of the output file
-# transformContext: Datum transformation settings
-# options: Save Options such as format, encoding etc.
-
-# Define the options for saving the layer
-save_options = QgsVectorFileWriter.SaveVectorOptions()
-save_options.driverName = 'CSV'
-save_options.fileEncoding = 'UTF-8'
-# We can also add some format-specific layer options 
-# These come from GDAL/OGR
-# https://gdal.org/drivers/vector/csv.html
-save_options.layerOptions = ['SEPARATOR=COMMA']
-
-# Write the file
-writer = QgsVectorFileWriter.create(
-    fileName=output_path,
-    fields=layer.fields(),
-    geometryType=QgsWkbTypes.NoGeometry,
-    srs=layer.crs(),
-    transformContext=transform_context,
-    options=save_options)
-
-# Check if we were able to create the writer
-if writer.hasError() != QgsVectorFileWriter.NoError:
-    iface.messageBar().pushMessage(
-        'Error:', writer.errorMessage, level=Qgis.Critical)
-
-selected_count = layer.selectedFeatureCount()
-if selected_count == 0:
-    iface.messageBar().pushMessage(
-        'Error:', 'No selected features', level=Qgis.Critical)
-else:
-    for f in layer.selectedFeatures():
-        writer.addFeature(f)
-
-    # delete the writer to flush features to disk
-    del writer
-    iface.messageBar().pushMessage(
-    'Success:',
-    f'Output file with {selected_count} features written at {output_path}',
-    level=Qgis.Success)
+print(field_names)

code/pyqgis/solutions/exercise9.py

@@ -0,0 +1,64 @@
+import os
+import time
+
+data_dir = os.path.join(os.path.expanduser('~'), 'Downloads', 'pyqgis_masterclass')
+
+layer = iface.activeLayer()
+
+# Check if a layer is selected
+if not layer:
+    iface.messageBar().pushMessage('Please select a layer',  level=Qgis.Critical) 
+# Check if the selected layer is a vector layer
+if layer.type() != QgsMapLayer.VectorLayer:
+    iface.messageBar().pushMessage('Please select a vector layer',  level=Qgis.Critical)
+
+# Define parameters for QgsVectorFileWriter
+output_name = 'output.csv'
+output_path = os.path.join(data_dir, output_name)
+
+# We will use QgsVectorFileWriter.create() method
+# It takes the following parameters
+# fileName: Path to the file
+# fields: Fields to write
+# geometryType: geometry type of output file
+# srs: CRS of the output file
+# transformContext: Datum transformation settings
+# options: Save Options such as format, encoding etc.
+
+# Define the options for saving the layer
+save_options = QgsVectorFileWriter.SaveVectorOptions()
+save_options.driverName = 'CSV'
+save_options.fileEncoding = 'UTF-8'
+# We can also add some format-specific layer options 
+# These come from GDAL/OGR
+# https://gdal.org/drivers/vector/csv.html
+save_options.layerOptions = ['SEPARATOR=COMMA']
+
+# Write the file
+writer = QgsVectorFileWriter.create(
+    fileName=output_path,
+    fields=layer.fields(),
+    geometryType=QgsWkbTypes.NoGeometry,
+    srs=layer.crs(),
+    transformContext=transform_context,
+    options=save_options)
+
+# Check if we were able to create the writer
+if writer.hasError() != QgsVectorFileWriter.NoError:
+    iface.messageBar().pushMessage(
+        'Error:', writer.errorMessage, level=Qgis.Critical)
+
+selected_count = layer.selectedFeatureCount()
+if selected_count == 0:
+    iface.messageBar().pushMessage(
+        'Error:', 'No selected features', level=Qgis.Critical)
+else:
+    for f in layer.selectedFeatures():
+        writer.addFeature(f)
+
+    # delete the writer to flush features to disk
+    del writer
+    iface.messageBar().pushMessage(
+    'Success:',
+    f'Output file with {selected_count} features written at {output_path}',
+    level=Qgis.Success)