Python 补丁项目分配

Question

假设有人想将 项目分配 添加到来自外国图书馆的 class 实例：

# defined outside our code base
class WeDoNotWantToDeriveThis(object): pass


inst = WeDoNotWantToDeriveThis()
def set_item_func(self, idx, val): print("hi there")
import types
# try to patch item setter
inst.__setitem__ = types.MethodType(set_item_func, inst)
assert hasattr(inst, '__setitem__')
print(type(inst.__setitem__)) # prints "instancemethod"
# try to perform item assignment on inst
inst[0] = None # raises 'object does not support item assignment'

问题是如何正确地做到这一点。也许'setitem'不是在实例上查找，而是在class本身上查找对象是否支持项目分配？

根据文档，实施 setitem 方法应该就足够了： https://docs.python.org/3/reference/datamodel.html#object.setitem

Answer 1

您必须在 class:

上设置实例方法

>>> WeDoNotWantToDeriveThis.__setitem__ = types.MethodType(set_item_func, None, WeDoNotWantToDeriveThis)
>>> inst[0] = None
hi there
>>>

Python 补丁项目分配

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