def METHOD_NAME(expr):
    """ convert the sympy sum to the
        pyccel node FunctionalSum
    """
    if not(isinstance(expr, Assign) and isinstance(expr.rhs, Sum)):
        return expr
    lhs = expr.lhs
    expr = expr.rhs
    index = expr.args[1]
    target = Function('range')(index[1], index[2])
    body = AugAssign(lhs, '+', expr.args[0])
    stmt = For(index[0], target, [body], strict=False)
    stmt = FunctionalSum([stmt], expr.args[0], lhs)
    return stmt