 Python does not support tail call optimization or first @-@ class continuations , and , according to Guido van Rossum , it never will . However , better support for <unk> @-@ like functionality is provided in 2 @.@ 5 , by extending Python 's generators . Before 2 @.@ 5 , generators were lazy <unk> ; information was passed unidirectionally out of the generator . As of Python 2 @.@ 5 , it is possible to pass information back into a generator function , and as of Python 3 @.@ 3 , the information can be passed through multiple stack levels . 
