I use closures quite a lot in python, but the variable lifetime semantics of closures are undocumented as far as I can tell. For example, consider the following code:

    def f():
        a=1
        b=1
        def g():
            return b
        return g

If we call ‘f’ and store the value, ‘b’ will be kept alive. Is ‘a’ kept alive? A naive implementation of closures might store a reference to the entire stack frame of ‘f’ inside the ‘g’ closure, causing ‘a’ to live even though it will never be used. This would be very bad, since generating a closure inside a long function could potentially cause a large memory leak. I wouldn’t expect this since python is implemented by smart people, but it’s worth checking.