let foo = a();
  let foo = b(foo);
  let fop = c(foo);
  let foo = d(foo);

Auto completion, highlight matching variable, gray out unread variables and warning of unused assignment.

I’ve written lots of python and can’t recall ever having this issue. More likely is a logic typo of two similar variables like length_x vs length_y, where a “let” wouldn’t have saved you anyway if both are already defined.

JavaScript, pre strict TS, on the other hand, where missing var implied global was a real motherload of bugs. Or kotlins “val” vs “var” changing semantics completely…wow. But those are different concepts from basic definition I know.