How to change colors for layers?

Question

How to save changing of colors?

For example, we change color for all features of a layer in a loop. But as a result, I see only latest changing.

My code does not work perfectly:

for k in masLevel:          
    iface.mapCanvas().setSelectionColor( QColor(colours[k-1]) )
    #filter features to select
    expr = QgsExpression( "\"Order\"='%d'"%int(k) )
    it = rivers.getFeatures( QgsFeatureRequest( expr ) )
    ids = [i.id() for i in it]
    rivers.setSelectedFeatures( ids )
    rivers.triggerRepaint()
    rivers.commitChanges()

Could you help me?

Answer 1

From comments, it seems that you want to apply a categorized renderer. A loop like yours is not necessary (unless there are other needs that you haven't explained in your original question).

You may use the following code as a reference (adapt it to your specific case):

from qgis.core import *
from PyQt4.QtGui import QColor

layer = iface.activeLayer() # load the layer as you want

# define the lookup >> value : (color, label)
colors = {1: ('red', 'some_text_for_red'), 2: ('yellow', 'some_text_for_yellow'), 3: ('cyan', 'some_text_for_cyan'), 4: ('green', 'some_text_for_green'), 5: ('blue', 'some_text_for_blue'), 6: ('magenta', 'some_text_for_magenta'), 7: ('grey', 'some_text_for_grey')}

# create a category for each item in your layer
categories = []
for value, (color, label) in colors.items():
    symbol = QgsSymbolV2.defaultSymbol(layer.geometryType())
    symbol.setColor(QColor(color))
    category = QgsRendererCategoryV2(value, symbol, label)
    categories.append(category)

# create the renderer and assign it to the layer
expression = 'my_field' # field name
renderer = QgsCategorizedSymbolRendererV2(expression, categories)

renderer = QgsCategorizedSymbolRendererV2(expression, categories)
layer.setRendererV2(renderer)
layer.triggerRepaint()

It will return something like this: