Are tuples immutable?

[ichabod801]

By modifying an object / item in tuple I modify tuple itself.

I think this is your key misunderstanding. You are not modifying the tuple. The tuple in memory is completely unchanged. Glossing over implementation details, the tuple contained two things when created: an integer and a reference to (memory location of) a list. You changed the list by referencing it through the tuple. After that, the tuple is still the same. It contains the same integer, and the same memory location. What is at that memory location changed, but that did not involve any changes in what is stored in the tuple. It just looks like you did, because python shows you what is at the memory location instead of that memory location itself.