Recursion limit problems

[elventear]

On May 12, 12:25 am, "Gabriel Genellina" <gagsl-... at yahoo.com.ar>
wrote:
> En Fri, 11 May 2007 19:17:57 -0300, elventear <elvent... at gmail.com>  
> escribió:
> "The only required property is that objects which compare equal have the  
> same hash value; it is advised to somehow mix together (e.g., using  
> exclusive or) the hash values for the components of the object that also  
> play a part in comparison of objects. If a class does not define a  
> __cmp__() method it should not define a __hash__() operation either; if it  
> defines __cmp__() or __eq__() but not __hash__(), its instances will not  
> be usable as dictionary keys. If a class defines mutable objects and  
> implements a __cmp__() or __eq__() method, it should not implement  
> __hash__(), since the dictionary implementation requires that a key's hash  
> value is immutable (if the object's hash value changes, it will be in the  
> wrong hash bucket)."

Thanks for the information. I have a doubt regarding the wording in
the paragraph on top.

Since I am defining a hash for my object, it makes sense that I should
be able to define equality. But I am not sure about inequality, in my
specific case. The paragraph above mentions that __cmp__ should be
defined if I define a __hash__, but in the default behaviour of
__cmp__ inequality is included. So what should I do? Also why is
equality necessary to be defined? Do dicts only use __hash__ or do
they use equality as well?

Thanks!