The writeback-only-if-changed approach sounds like a plausible improvement to me. I'd be hesitant to include such a change in 3.5.4 though, since we don't get a second go at that if something breaks unexpectedly. However, I don't think returning a write-through proxy from locals() would be a good idea, since you can still have race conditions between "read-update-writeback" operations that affect the cells directly, as well as with those that use the new write-through proxy. At the moment, you can only get yourself into trouble by way of operations that have access to LocalsToFast, and those are pretty rare now that `exec` is no longer a statement. If folks really want that write-through behaviour (at least for closure variables), 3.7 will let them write it themselves, since closure cells are becoming writeable from pure Python code: >>> def outer(): ... x = 1 ... def inner(): ... return x ... return inner ... >>> f = outer() >>> f.__closure__[0].cell_contents 1 >>> f.__closure__[0].cell_contents = 2 >>> f() 2 >>> f.__closure__[0].cell_contents = "hello" >>> f() 'hello' ```