Security was not my primary concern, but even if the design can be made secure, it is still a concern (because bugs happen). In any case, you just stated anothe

Security was not my primary concern, but even if the design can be made secure, it is still a concern (because bugs happen). In any case, you just stated another counter argument - it breaks orthogonality of the language (string being interpolated must be a literal), just to make one assignment not explicit. Maybe it is popular in other languages - their call, but the fact is, it goes quite wildly against Python design philosophy. I would also like to note that the are templating systems that let you evaluate arbitrary Python expressions. Perhaps these would be a better choice for users who feel need for this proposal.