Is it a good idea to hash a Python class?
class, dictionary, hash, inheritance, python
Solution
Yes, any object that doesn't implement a `__hash__()` function will return its id when hashed. From Python Language Reference: Data Model - Basic Customization:
User-defined classes have `__cmp__()` and `__hash__()` methods by default; with them, all objects compare unequal (except with themselves) and `x.__hash__()` returns `id(x)`.
However, if you're looking to have a unique identifier, use `id` to be clear about your intent. A hash of an object should be a combination of the hashes of its components. See the above link for more details.
Problem
For example, suppose I do this: ``` >>> class foo(object): ... pass ... >>> class bar(foo): ... pass ... >>> some_dict = { foo : 'foo', ... bar : 'bar'} >>> >>> some_dict[bar] 'bar' >>> some_dict[foo] 'foo' >>> hash(bar) 165007700 >>> id(bar) 165007700 ``` Based on that, it looks like the class is getting hashed as its id number. Therefore, there shouldn't be any danger of worrying about, say, a `bar` hashing as either a `foo` or a `bar` or hash values changing if I mutate the class. Is this behavior reliable, or are there any gotchas here?