Bug report

I'm trying to use a python virtual environment in my colcon workspace to separate system level and node level dependencies. I'm following the instructions given in this tutorial in the ros2 documentation (Specifically installing via a virtual environment). However, when I check what python interpreter is being used inside the node, it returns the system level one instead of the virtual environment. This can be further verified by installing a package in the virtual environment that is not present in the system environment and try importing it from inside the node.

I have tried doing a clean build with and without sourcing the virtual environment in the build shell. I have also tried using virtualenv as in the tutorial and also python -m venv. I also call my virtual environment "venv" as in the tutorial.

Required Info:

• Operating System: Ubuntu 20.04
• Installation type: Binaries
• Version or commit hash: Foxy Fitzroy
• DDS implementation: (Default) Cyclone DDS
• Client library (if applicable): N/A

Steps to reproduce issue

1. Follow the steps in the tutorial
2. Create a ros2 python package with cd src && ros2 pkg create venv --build-type ament_python
3. Create a python node called venv.py under src/venv/venv with the following code

import rclpy
from rclpy.node import Node
import sys

class ExampleNode(Node):
    def __init__(self):
        super().__init__('sensors')
        self.get_logger().info("ExampleNode started")
        self.get_logger().info(f"python path: {sys.executable}")

def main(args=None):
    rclpy.init(args=args)
    node = ExampleNode()
    rclpy.spin(node)
    rclpy.shutdown()

if __name__ == '__main__':
    main()

4. Add the node to setup.py with

entry_points={
      'console_scripts': [
          'venv = venv.venv:main'
      ],
  },

5. Build using

source ./venv/bin/activate
source /opt/ros/foxy/setup.bash
colcon build
source install/setup.sh

6. Run using ros2 run venv venv

Expected behavior

The returned python path should show ${workspaceFolder}/venv/bin/python and any packages installed in the virtual environment should be accessible inside the node.

Actual behavior

Returns the system base python /usr/bin/python3 and breaks when trying to import a package that is installed in the virtual environment but not at system level.