Let's not confuse matters here: in both those languages an initialization-assignment will introduce a new binding within function scopes. In CoffeeScript it will always be the parent scope's binding, which means that you must take extra care not to introduce variables used in scopes above, or below, at any given time.

On the other hand, confusing both concepts is bad because it makes it harder to reason about scope, and it has been the cause of much confusion regarding closures in Python and Ruby.

Lua has perfectly sane lexical scope for its local variables. Don't mix it with Python and Coffeescript.