caching attribute reference

[Ofnuts]

it might come down to the CPU cost of .attribute vs a plain local variable.  given that self is a local variable there is already the cost of accessing self.  now add on the cost of accessing an attribute within it ... unless python does any performance optimizing for self specifically (because it is so commonly used) or for repeating expressions.

It is highly likely that the compiler recognizes the pattern and optimizes around it (assuming it is worth it). Using your own variable may make it less obvious and prevent better optimizations.