human
Complete the below
def copy_doc(source):

    ''''Copy the docstring from another function (decorator).
    The docstring of the source function is prepepended to the docstring of the
    function wrapped by this decorator.
    This is useful when inheriting from a class and overloading a method. This
    decorator can be used to copy the docstring of the original method.
    Parameters
    source : function
    Function to copy the docstring from
    Returns
    wrapper : function
    The decorated function
    Examples
    >>> class A:
    ...     def m1():
    ...         \'\'\'Docstring for m1\'\'\'
    ...         pass
    >>> class B (A):
    ...     @copy_doc(A.m1)
    ...     def m1():
    ...         \'\'\' this gets appended\'\'\'
    ...         pass
    >>> print(B.m1.__doc__)
    Docstring for m1 this gets appended'
    '''
assistant
#Here is the Python program you requested.
    def wrapper(func):
        if ((source.__doc__ is None) or (len(source.__doc__) == 0)):
            raise ValueError('Cannot    copy    docstring:    docstring    was    empty.')
        doc = source.__doc__
        if (func.__doc__ is not None):
            doc += func.__doc__
        func.__doc__ = doc
        return func
    return wrapper