qgis - How to set Marker Line symbol for QgsVectorLayer by using Python?

QgsVectorLayer Right click->Properties->Style->Single symbol->click on simple line in tree node ->symbol layer type -> Marker line

Kindly help me to set marker line symbol programmatically by using Python.

Answer

The only documentation I found is here, but it doesn't help much in practice.

Here is an example I used to set the renderer of the current layer to a symbol with two layers: one 'Simple Line' and one 'Marker Line'. The marker line is tricky, because you need to work with a subSymbol.

# Use the currently selected layer
layer = qgis.utils.iface.mapCanvas().currentLayer()

registry = QgsSymbolLayerV2Registry.instance()

lineMeta = registry.symbolLayerMetadata("SimpleLine")
markerMeta = registry.symbolLayerMetadata("MarkerLine")

symbol = QgsSymbolV2.defaultSymbol(layer.geometryType())

# Line layer
lineLayer = lineMeta.createSymbolLayer({'width': '0.26', 'color': '255,0,0', 'offset': '-1.0', 'penstyle': 'solid', 'use_custom_dash': '0', 'joinstyle': 'bevel', 'capstyle': 'square'})

# Marker layer
markerLayer = markerMeta.createSymbolLayer({'width': '0.26', 'color': '255,0,0', 'interval': '3', 'rotate': '1', 'placement': 'interval', 'offset': '-1.0'})

subSymbol = markerLayer.subSymbol()
# Replace the default layer with our own SimpleMarker
subSymbol.deleteSymbolLayer(0)
triangle = registry.symbolLayerMetadata("SimpleMarker").createSymbolLayer({'name': 'filled_arrowhead', 'color': '255,0,0', 'color_border': '0,0,0', 'offset': '0,0', 'size': '1.5', 'angle': '0'})
subSymbol.appendSymbolLayer(triangle)

# Replace the default layer with our two custom layers
symbol.deleteSymbolLayer(0)
symbol.appendSymbolLayer(lineLayer)
symbol.appendSymbolLayer(markerLayer)


# Replace the renderer of the current layer
renderer = QgsSingleSymbolRendererV2(symbol)
layer.setRendererV2(renderer)

You can also inspect (and probably modify) the symbols for a layer, for example:

layer.rendererV2().symbol().symbolLayer(0).properties()