我可以在Python中使用对象(类的实例)作为字典键吗? [英] Can I use an object (an instance of a class) as a dictionary key in Python?

问题描述

我想将类实例用作字典键，例如:

I want to use a class instance as a dictionary key, like:

classinstance = class()
dictionary[classinstance] = 'hello world'

Python似乎无法将类作为字典键处理，还是我错了? 此外，我可以使用[[(classinstance，helloworld)，...]之类的元组列表代替字典，但这看起来非常不专业. 您是否有解决此问题的线索?

Python seems to be not able to handle classes as dictionary key, or am I wrong? In addition, I could use a Tuple-list like [(classinstance, helloworld),...] instead of a dictionary, but that looks very unprofessional. Do you have any clue for fixing that issue?

推荐答案

您的实例需要可哈希化. Python词汇表告诉我们:

Your instances need to be hashable. The python glossary tells us:

如果对象的哈希值在其生命周期内始终不变(需要使用__hash__()方法)，并且可以与其他对象进行比较(需要使用__eq__()或__cmp__()方法)，则该对象是可哈希的.比较相等的可哈希对象必须具有相同的哈希值.

An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() or __cmp__() method). Hashable objects which compare equal must have the same hash value.

可哈希性使对象可用作字典键和set成员，因为这些数据结构在内部使用哈希值.

Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.

Python的所有不可变内置对象都是可哈希的，而没有可变容器(例如列表或字典)是可哈希的.默认情况下，作为用户定义类实例的对象是可哈希的.它们都比较不相等，并且其哈希值是其id().

All of Python’s immutable built-in objects are hashable, while no mutable containers (such as lists or dictionaries) are. Objects which are instances of user-defined classes are hashable by default; they all compare unequal, and their hash value is their id().

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