import math


def angle3pt(a: tuple, b: tuple, c: tuple) -> float:
    """
    Calculate the angle by turning from coordinate a to c around b.

    :param a:             coordinate a (x, y)
    :param b:             coordinate b (x, y)
    :param c:             coordinate c (x, y)
    :returns:
        * **ang** -       angle between a and c

    """

    ang = math.atan2(c[1] - b[1], c[0] - b[0]) - math.atan2(a[1] - b[1], a[0] - b[0])

    if ang > math.pi:
        ang -= 2 * math.pi
    elif ang <= -math.pi:
        ang += 2 * math.pi

    return ang