what is :exception in a doc string python code example

Example: what is :exception in a doc string python

def func(arg1, arg2):
    """Summary line.

    Extended description of function.

    :param int arg1: Description of arg1.
    :param str arg2: Description of arg2.
    :raise: ValueError if arg1 is equal to arg2
    :return: Description of return value
    :rtype: bool

    :example:

    >>> a=1
    >>> b=2
    >>> func(a,b)
    True
    """

    if arg1 == arg2:
        raise ValueError('arg1 must not be equal to arg2')

    return True