I am mostly interested in terms of what is happening but lets say I have a custom class with __eq__ implemented and nothing else.
How do the other comparisons get resolved? What is the default behaviour? Every time I run the comparison I get a different result. I know that I need to implement these and that I can also use @total_ordering to simplify the job.
What is actually happening behind the scenes? This is mostly out curiosity.
If __lt__ isn't defined, comparisons use __cmp__ instead. If that's not defined, it uses a default comparator. And it appears that the default comparator compares by "object identity (address)".
See the docs for __cmp__ for details.
Some additional information from this section of the Python documentation:
Objects of different types, except different numeric types and different string types, never compare equal; such objects are ordered consistently but arbitrarily (so that sorting a heterogeneous array yields a consistent result).
CPython implementation detail: Objects of different types except numbers are ordered by their type names; objects of the same types that don’t support proper comparison are ordered by their address.
