Dictionary comparison?

[brainstaurm]

I would like to understand the internals of the dictionary comparison in python.

The python reference manual says that:
"If a class does not define a __cmp__() method it should not define a __hash__() operation either". Why does this dependency exist?

I tried to google for it, but couldn't find proper documentation. Any pointers will be helpful.

Thank you!

[bvdet]

I would like to understand the internals of the dictionary comparison in python.

The python reference manual says that:
"If a class does not define a __cmp__() method it should not define a __hash__() operation either". Why does this dependency exist?

I tried to google for it, but couldn't find proper documentation. Any pointers will be helpful.

Thank you!

From Python Essential Reference: ...mutable objects should not define this method (__hash__()); any changes to an object will alter their hash value and make it impossible to locate an object on subsequent dictionary lookups. An object should not define a __hash__() method without also defining __cmp__().

[bartonc]

From Python Essential Reference: ...mutable objects should not define this method (__hash__()); any changes to an object will alter their hash value and make it impossible to locate an object on subsequent dictionary lookups. An object should not define a __hash__() method without also defining __cmp__().

I take it that __cmp__() is used by __hash__() in its search.

[bvdet]

I take it that __cmp__() is used by __hash__() in its search.

Take a look at the explanation in the General Python FAQ: LINK