Instances as dictionary key, __hash__ and __eq__

Jean-Michel Pichavant jeanmichel at sequans.com
Tue Feb 19 11:11:57 CET 2013


> > Additionally, If I'm making things much more complicated than they
> > need to be, let me know.
> 

> You are. There are ways to achieve what you want, but it requires a
> lot more setup and discipline. The simplest way is probably to have
> a _equal_fields() method that subclasses override, returning a tuple
> of the attributes that should be hashed. Then in __hash__() and
> __eq__ you iterate over the returned tuple, get the value for each
> attribute and either hash or compare.

> Of course, you have to take into account in __eq__ that the other
> instance may not have the same attributes (e.g. self is a subclass
> that uses extra attributes in its __hash__ and __eq__).

> Tim Delaney

I will happily restrain myself to never subclass such class.

JM


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