In Python you can't have "if x = 3:" ... that's a syntax error. And Python also uses "==" for equality comparison.
There, problem solved.
I would solve the problem in Obj-C by introducing a directive on the file-level for the newer syntax, like how they did it in F# with the "#light" directive. And when a file is compiled with that directive, the compiler could trigger compile-time errors for those obviously dangerous constructs.