ROS2 euler to quaternion transformation.

euler_from_quaternion.py

def euler_from_quaternion(quaternion):
    """
    Converts quaternion (w in last place) to euler roll, pitch, yaw
    quaternion = [x, y, z, w]
    Bellow should be replaced when porting for ROS 2 Python tf_conversions is done.
    """
    x = quaternion.x
    y = quaternion.y
    z = quaternion.z
    w = quaternion.w

    sinr_cosp = 2 * (w * x + y * z)
    cosr_cosp = 1 - 2 * (x * x + y * y)
    roll = np.arctan2(sinr_cosp, cosr_cosp)

    sinp = 2 * (w * y - z * x)
    pitch = np.arcsin(sinp)

    siny_cosp = 2 * (w * z + x * y)
    cosy_cosp = 1 - 2 * (y * y + z * z)
    yaw = np.arctan2(siny_cosp, cosy_cosp)

    return roll, pitch, yaw

quaternion_from_euler.py

def quaternion_from_euler(roll, pitch, yaw):
    """
    Converts euler roll, pitch, yaw to quaternion (w in last place)
    quat = [x, y, z, w]
    Bellow should be replaced when porting for ROS 2 Python tf_conversions is done.
    """
    cy = math.cos(yaw * 0.5)
    sy = math.sin(yaw * 0.5)
    cp = math.cos(pitch * 0.5)
    sp = math.sin(pitch * 0.5)
    cr = math.cos(roll * 0.5)
    sr = math.sin(roll * 0.5)

    q = [0] * 4
    q[0] = cy * cp * cr + sy * sp * sr
    q[1] = cy * cp * sr - sy * sp * cr
    q[2] = sy * cp * sr + cy * sp * cr
    q[3] = sy * cp * cr - cy * sp * sr

    return q

quaternion_from_euler results are inconsistent with docstring
q[0] is w
q[1] is x
q[2] is y
q[3] is z

yes,as my test,quaternion_from_euler result is 'w' in first place,so it is [w,x,y,z]

Yes, thanks for noticing.
The correct info should be:

    """
    Converts quaternion (w in last place) to euler roll, pitch, yaw
    quaternion = [w, x, y, z]
    Bellow should be replaced when porting for ROS 2 Python tf_conversions is done.
    """

There is https://discourse.ros.org/t/tf-transformations-ros-2-python-package-for-easy-tf-math/21077
Github: https://github.com/DLu/tf_transformations/

Usage http://docs.ros.org/en/rolling/Tutorials/Tf2/Writing-A-Tf2-Broadcaster-Py.html#writingatf2broadcasterpy

sudo apt install ros-foxy-tf-transformations
sudo pip3 install transforms3d

import tf_transformations
q = tf_transformations.quaternion_from_euler(r, p, y)
r, p, y = tf_transformations.euler_from_quaternion(quaternion)

Thanks, @Darkproduct. However, your proposed solutions are not available yet for Debian.

In the meantime, I have included a class to avoid the confusion with the indexes and the order of x, y, z, w:

class Quaternion:
    w: float
    x: float
    y: float
    z: float

def quaternion_from_euler(roll, pitch, yaw):
    """
    Converts euler roll, pitch, yaw to quaternion
    """
    cy = math.cos(yaw * 0.5)
    sy = math.sin(yaw * 0.5)
    cp = math.cos(pitch * 0.5)
    sp = math.sin(pitch * 0.5)
    cr = math.cos(roll * 0.5)
    sr = math.sin(roll * 0.5)

    q = Quaternion()
    q.w = cy * cp * cr + sy * sp * sr
    q.x = cy * cp * sr - sy * sp * cr
    q.y = sy * cp * sr + cy * sp * cr
    q.z = sy * cp * cr - cy * sp * sr
    return q