Lua's ability to bind a closure to a mutable variable is a very powerful ability that I use all the time. But due to the way loop variables are handled, the example that's "broken" in Python works "as expected" in Lua:

  fns = {}
  
  for i=1,10 do
    fns[i]= function() return i; end
  end
  
  for i=1,10 do
    print("fns[i]",fns[i]())
  end

This produces:

  fns[i] 1
  fns[i] 2
  fns[i] 3
  fns[i] 4
  fns[i] 5
  fns[i] 6
  fns[i] 7
  fns[i] 8
  fns[i] 9
  fns[i] 10

If you change the set-up loop to look like this, though:

  local j
  for i=1,10 do
    j=i
    fns[i]= function() return i,j; end
  end

...then it prints:

  fns[i] 1 10
  fns[i] 2 10
  fns[i] 3 10
  fns[i] 4 10
  fns[i] 5 10
  fns[i] 6 10
  fns[i] 7 10
  fns[i] 8 10
  fns[i] 9 10
  fns[i] 10 10

In that case, it has bound the mutable "j" to each of the 10 closures, though you can see it's created a new binding for i on each pass through the loop. It WILL create a new instance of the mutable "j" each time "local j" is executed, though, so if the above code is in a function or another block that's executed more than once, then each time those functions will be bound to a new "j".

EDIT: Get the code markup right.