Iterating over line features to change colors using PyQGIS

Question

I want to iterate over line features to change color of each feature to the color I choose. So my file has 7 features, I want am writing the code below, but it does not seem to work.

line_feats = [f for f in line_layer.getFeatures()]
clr = ["blue","red","green","yellow","magenta","cyan","black","red"]
for l in line_feats:
    line_layer.select(l.id())
    iface.mapCanvas().setSelectionColor( QColor(clr[l.id()]))
line_layer.triggerRepaint()

I have tried printing l.id() and it goes from 0 to 7, so indexing is not the issue. The thing is, it does not change the color individually, rather it changes for the entire file.

Answer 1

It seems what you want to do is not a "selection" but a "symbology". Because for selection, there is only a single color available for the whole QGIS project. You can find the selection color in QGIS Project settings, "General" tab.

You want to do a Categorized Rendering, which is in the Layer Properties, "Symbology" tab. To do that from PyQGIS, using feature ID as you have mentionned :

color = ["blue","red","green","yellow","magenta","cyan","black","red"]

categories = []
for i, value in enumerate(color):
    symbol = QgsSymbol.defaultSymbol(QgsWkbTypes.LineGeometry)
    symbol.setColor(QColor(value))
    category = QgsRendererCategory(str(i), symbol, value)
    categories.append(category)

renderer = QgsCategorizedSymbolRenderer('$id', categories)
iface.activeLayer().setRenderer(renderer)

Open the layer properties, "Symbology" tab after this script to check the result.