Drawing polyline with user input points in QGIS using Python

Question

I have an empty layer in QGIS in that i just want to draw a polyline by selecting points on layer using Python.

For example, if I select a start point and endpoint on a layer, I want to draw a line connecting to those points using Python code. I have gone through all related references but I didn't get it.

What I have tried is:

from qgis.gui import QgsMapToolEmitPoint

def display_point(point, mouse_button):
  coords = "Map Coordinates: {:.4f}, {:.4f}".format(point.x(), point.y())
  print coords
  
  layer = iface.activeLayer()
  feats = [ feat for feat in layer.getFeatures() ]
  geo_pt = QgsGeometry.fromPoint(QgsPoint(point.x(), point.y()))
  id = -1

  for feat in feats:
    if geo_pt.within(feat.geometry()):
      id = feat.id()
      break

  if id != -1:
    print feats[id].attribute('name')
  else:
    print "no feature selected"

canvas = iface.mapCanvas()
pointTool = QgsMapToolEmitPoint(canvas)
pointTool.canvasClicked.connect(display_point)
canvas.setMapTool(pointTool)

Answer 1

You could try to identify the selected features of the source layer with

sourceLayer.getSelectedFeatures()

and then create a line geometry from the list of points:

line = QgsGeometry.fromPolyline(list_of_points)