How to "append" to personalised ROS array message in python

Question

I defined the two following message structures for a ROS package:

point.msg

float64 x
float64 y

points.msg

point[] points

I am instantiating and filling a points array in Python as follows:

point_list = points()
pt = point()
for element in self.points:
     pt.x = element[0,0]
     pt.y = element[1,0]
     point_list += (pt,)

And this is the error I am getting:

unsupported operand type(s) for +=: 'points' and 'tuple'

PS : tried .append and it is still not working

Answer 1

The message points is not directly a list of point messages, but a structure, that has a member called points which is a list.

To add elements to this list, you have to access the member, not the containing structure:

point_list.points.append(pt)