IPython"Canary Method"的含义以及如果它存在会发生什么？

Question

IPython源代码包括一个getattr检查函数'_ipython_canary_method_should_not_exist_'开头是否存在的检查get_real_method:

def get_real_method(obj, name):
    """Like getattr, but with a few extra sanity checks:
    - If obj is a class, ignore everything except class methods
    - Check if obj is a proxy that claims to have all attributes
    - Catch attribute access failing with any exception
    - Check that the attribute is a callable object
    Returns the method or None.
    """
    try:
        canary = getattr(obj, '_ipython_canary_method_should_not_exist_', None)
    except Exception:
        return None

    if canary is not None:
        # It claimed to have an attribute it should never have
        return None

虽然很容易找到其他编码器特别设置这个名称,但更难找到任何有意义的解释原因.

鉴于这两个类:

from __future__ import print_function

class Parrot(object):
    def __getattr__(self, attr):
        print(attr)
        return lambda *a, **kw: print(attr, a, kw)

class DeadParrot(object):
    def __getattr__(self, attr):
        print(attr)
        if attr == '_ipython_canary_method_should_not_exist_':
            raise AttributeError(attr)
        return lambda *a, **kw: print(attr, a, kw)

似乎IPython正在使用此方法的存在或缺乏来决定是使用repr还是使用其丰富的显示方法之一.故意阻止测试DeadParrot会导致IPython查找并调用_repr_mimebundle_.

我正在写一个假装所有attrs存在的对象.我如何决定是否特殊情况呢？