<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def builtin_folding(value):
 """ Convert builtin function to ast expression. """

    if isinstance(value, (type(None), bool)):
        name = str(value)
    elif value.__name__ in ("bool", "float", "int"):
        name = value.__name__ + "_"
    else:
        name = value.__name__
    return ast.Attribute(ast.Name('__builtin__', ast.Load(), None),
                         name, ast.Load())